I have an object that contains an array of objects.
obj = {};
obj.arr = new Array();
obj.arr.push({place:"here",name:"stuff"});
obj.arr.push({place:"there",name:"morestuff"});
obj.arr.push({place:"there",name:"morestuff"});
I'm wondering what is the best method to remove duplicate objects from an array. So for example, obj.arr would become...
{place:"here",name:"stuff"},
{place:"there",name:"morestuff"}
How about with some es6 magic?
obj.arr = obj.arr.filter((value, index, self) =>
index === self.findIndex((t) => (
t.place === value.place && t.name === value.name
))
)
Reference URL
A more generic solution would be:
const uniqueArray = obj.arr.filter((value, index) => {
const _value = JSON.stringify(value);
return index === obj.arr.findIndex(obj => {
return JSON.stringify(obj) === _value;
});
});
Using the above property strategy instead of JSON.stringify:
const isPropValuesEqual = (subject, target, propNames) =>
propNames.every(propName => subject[propName] === target[propName]);
const getUniqueItemsByProperties = (items, propNames) =>
items.filter((item, index, array) =>
index === array.findIndex(foundItem => isPropValuesEqual(foundItem, item, propNames))
);
You can add a wrapper if you want the propNames property to be either an array or a value:
const getUniqueItemsByProperties = (items, propNames) => {
const propNamesArray = Array.from(propNames);
return items.filter((item, index, array) =>
index === array.findIndex(foundItem => isPropValuesEqual(foundItem, item, propNamesArray))
);
};
allowing both getUniqueItemsByProperties('a') and getUniqueItemsByProperties(['a']);
Stackblitz Example
Explanation
Start by understanding the two methods used:
filter, findIndex
Next take your idea of what makes your two objects equal and keep that in mind.
We can detect something as a duplicate, if it satisfies the criterion that we have just thought of, but it's position is not at the first instance of an object with the criterion.
Therefore we can use the above criterion to determine if something is a duplicate.
One liners with filter ( Preserves order )
Find unique id's in an array.
arr.filter((v,i,a)=>a.findIndex(v2=>(v2.id===v.id))===i)
If the order is not important, map solutions will be faster: Solution with map
Unique by multiple properties ( place and name )
arr.filter((v,i,a)=>a.findIndex(v2=>['place','name'].every(k=>v2[k] ===v[k]))===i)
Unique by all properties (This will be slow for large arrays)
arr.filter((v,i,a)=>a.findIndex(v2=>(JSON.stringify(v2) === JSON.stringify(v)))===i)
Keep the last occurrence by replacing findIndex with findLastIndex.
arr.filter((v,i,a)=>a.findLastIndex(v2=>(v2.place === v.place))===i)
Using ES6+ in a single line you can get a unique list of objects by key:
const key = 'place';
const unique = [...new Map(arr.map(item => [item[key], item])).values()]
It can be put into a function:
function getUniqueListBy(arr, key) {
return [...new Map(arr.map(item => [item[key], item])).values()]
}
Here is a working example:
const arr = [
{place: "here", name: "x", other: "other stuff1" },
{place: "there", name: "x", other: "other stuff2" },
{place: "here", name: "y", other: "other stuff4" },
{place: "here", name: "z", other: "other stuff5" }
]
function getUniqueListBy(arr, key) {
return [...new Map(arr.map(item => [item[key], item])).values()]
}
const arr1 = getUniqueListBy(arr, 'place')
console.log("Unique by place")
console.log(JSON.stringify(arr1))
console.log("\nUnique by name")
const arr2 = getUniqueListBy(arr, 'name')
console.log(JSON.stringify(arr2))
How does it work
First the array is remapped in a way that it can be used as an input for a Map.
arr.map(item => [item[key], item]);
which means each item of the array will be transformed in another array with 2 elements; the selected key as first element and the entire initial item as second element, this is called an entry (ex. array entries, map entries). And here is the official doc with an example showing how to add array entries in Map constructor.
Example when key is place:
[["here", {place: "here", name: "x", other: "other stuff1" }], ...]
Secondly, we pass this modified array to the Map constructor and here is the magic happening. Map will eliminate the duplicate keys values, keeping only last inserted value of the same key.
Note: Map keeps the order of insertion. (check difference between Map and object)
new Map(entry array just mapped above)
Third we use the map values to retrieve the original items, but this time without duplicates.
new Map(mappedArr).values()
And last one is to add those values into a fresh new array so that it can look as the initial structure and return that:
return [...new Map(mappedArr).values()]
Simple and performant solution with a better runtime than the 70+ answers that already exist:
const ids = array.map(o => o.id)
const filtered = array.filter(({id}, index) => !ids.includes(id, index + 1))
Example:
const arr = [{id: 1, name: 'one'}, {id: 2, name: 'two'}, {id: 1, name: 'one'}]
const ids = arr.map(o => o.id)
const filtered = arr.filter(({id}, index) => !ids.includes(id, index + 1))
console.log(filtered)
How it works:
Array.filter() removes all duplicate objects by checking if the previously mapped id-array includes the current id ({id} destructs the object into only its id). To only filter out actual duplicates, it is using Array.includes()'s second parameter fromIndex with index + 1 which will ignore the current object and all previous.
Since every iteration of the filter callback method will only search the array beginning at the current index + 1, this also dramatically reduces the runtime because only objects not previously filtered get checked.
This obviously also works for any other key that is not called id, multiple or even all keys.
A primitive method would be:
const obj = {};
for (let i = 0, len = things.thing.length; i < len; i++) {
obj[things.thing[i]['place']] = things.thing[i];
}
things.thing = new Array();
for (const key in obj) {
things.thing.push(obj[key]);
}
If you can use Javascript libraries such as underscore or lodash, I recommend having a look at _.uniq function in their libraries. From lodash:
_.uniq(array, [isSorted=false], [callback=_.identity], [thisArg])
Basically, you pass in the array that in here is an object literal and you pass in the attribute that you want to remove duplicates with in the original data array, like this:
var data = [{'name': 'Amir', 'surname': 'Rahnama'}, {'name': 'Amir', 'surname': 'Stevens'}];
var non_duplidated_data = _.uniq(data, 'name');
UPDATE: Lodash now has introduced a .uniqBy as well.
I had this exact same requirement, to remove duplicate objects in a array, based on duplicates on a single field. I found the code here: Javascript: Remove Duplicates from Array of Objects
So in my example, I'm removing any object from the array that has a duplicate licenseNum string value.
var arrayWithDuplicates = [
{"type":"LICENSE", "licenseNum": "12345", state:"NV"},
{"type":"LICENSE", "licenseNum": "A7846", state:"CA"},
{"type":"LICENSE", "licenseNum": "12345", state:"OR"},
{"type":"LICENSE", "licenseNum": "10849", state:"CA"},
{"type":"LICENSE", "licenseNum": "B7037", state:"WA"},
{"type":"LICENSE", "licenseNum": "12345", state:"NM"}
];
function removeDuplicates(originalArray, prop) {
var newArray = [];
var lookupObject = {};
for(var i in originalArray) {
lookupObject[originalArray[i][prop]] = originalArray[i];
}
for(i in lookupObject) {
newArray.push(lookupObject[i]);
}
return newArray;
}
var uniqueArray = removeDuplicates(arrayWithDuplicates, "licenseNum");
console.log("uniqueArray is: " + JSON.stringify(uniqueArray));
The results:
uniqueArray is:
[{"type":"LICENSE","licenseNum":"10849","state":"CA"},
{"type":"LICENSE","licenseNum":"12345","state":"NM"},
{"type":"LICENSE","licenseNum":"A7846","state":"CA"},
{"type":"LICENSE","licenseNum":"B7037","state":"WA"}]
One liner using Set
var things = new Object();
things.thing = new Array();
things.thing.push({place:"here",name:"stuff"});
things.thing.push({place:"there",name:"morestuff"});
things.thing.push({place:"there",name:"morestuff"});
// assign things.thing to myData for brevity
var myData = things.thing;
things.thing = Array.from(new Set(myData.map(JSON.stringify))).map(JSON.parse);
console.log(things.thing)
Explanation:
new Set(myData.map(JSON.stringify)) creates a Set object using the stringified myData elements.
Set object will ensure that every element is unique.
Then I create an array based on the elements of the created set using Array.from.
Finally, I use JSON.parse to convert stringified element back to an object.
ES6 one liner is here
let arr = [
{id:1,name:"sravan ganji"},
{id:2,name:"pinky"},
{id:4,name:"mammu"},
{id:3,name:"avy"},
{id:3,name:"rashni"},
];
console.log(Object.values(arr.reduce((acc,cur)=>Object.assign(acc,{[cur.id]:cur}),{})))
To remove all duplicates from an array of objects, the simplest way is use filter:
var uniq = {};
var arr = [{"id":"1"},{"id":"1"},{"id":"2"}];
var arrFiltered = arr.filter(obj => !uniq[obj.id] && (uniq[obj.id] = true));
console.log('arrFiltered', arrFiltered);
One liners with Map ( High performance, Does not preserve order )
Find unique id's in array arr.
const arrUniq = [...new Map(arr.map(v => [v.id, v])).values()]
If the order is important check out the solution with filter: Solution with filter
Unique by multiple properties ( place and name ) in array arr
const arrUniq = [...new Map(arr.map(v => [JSON.stringify([v.place,v.name]), v])).values()]
Unique by all properties in array arr
const arrUniq = [...new Map(arr.map(v => [JSON.stringify(v), v])).values()]
Keep the first occurrence in array arr
const arrUniq = [...new Map(arr.slice().reverse().map(v => [v.id, v])).values()].reverse()
Here's another option to do it using Array iterating methods if you need comparison only by one field of an object:
function uniq(a, param){
return a.filter(function(item, pos, array){
return array.map(function(mapItem){ return mapItem[param]; }).indexOf(item[param]) === pos;
})
}
uniq(things.thing, 'place');
This is a generic way of doing this: you pass in a function that tests whether two elements of an array are considered equal. In this case, it compares the values of the name and place properties of the two objects being compared.
ES5 answer
function removeDuplicates(arr, equals) {
var originalArr = arr.slice(0);
var i, len, val;
arr.length = 0;
for (i = 0, len = originalArr.length; i < len; ++i) {
val = originalArr[i];
if (!arr.some(function(item) { return equals(item, val); })) {
arr.push(val);
}
}
}
function thingsEqual(thing1, thing2) {
return thing1.place === thing2.place
&& thing1.name === thing2.name;
}
var things = [
{place:"here",name:"stuff"},
{place:"there",name:"morestuff"},
{place:"there",name:"morestuff"}
];
removeDuplicates(things, thingsEqual);
console.log(things);
Original ES3 answer
function arrayContains(arr, val, equals) {
var i = arr.length;
while (i--) {
if ( equals(arr[i], val) ) {
return true;
}
}
return false;
}
function removeDuplicates(arr, equals) {
var originalArr = arr.slice(0);
var i, len, j, val;
arr.length = 0;
for (i = 0, len = originalArr.length; i < len; ++i) {
val = originalArr[i];
if (!arrayContains(arr, val, equals)) {
arr.push(val);
}
}
}
function thingsEqual(thing1, thing2) {
return thing1.place === thing2.place
&& thing1.name === thing2.name;
}
removeDuplicates(things.thing, thingsEqual);
If you can wait to eliminate the duplicates until after all the additions, the typical approach is to first sort the array and then eliminate duplicates. The sorting avoids the N * N approach of scanning the array for each element as you walk through them.
The "eliminate duplicates" function is usually called unique or uniq. Some existing implementations may combine the two steps, e.g., prototype's uniq
This post has few ideas to try (and some to avoid :-) ) if your library doesn't already have one! Personally I find this one the most straight forward:
function unique(a){
a.sort();
for(var i = 1; i < a.length; ){
if(a[i-1] == a[i]){
a.splice(i, 1);
} else {
i++;
}
}
return a;
}
// Provide your own comparison
function unique(a, compareFunc){
a.sort( compareFunc );
for(var i = 1; i < a.length; ){
if( compareFunc(a[i-1], a[i]) === 0){
a.splice(i, 1);
} else {
i++;
}
}
return a;
}
I think the best approach is using reduce and Map object. This is a single line solution.
const data = [
{id: 1, name: 'David'},
{id: 2, name: 'Mark'},
{id: 2, name: 'Lora'},
{id: 4, name: 'Tyler'},
{id: 4, name: 'Donald'},
{id: 5, name: 'Adrian'},
{id: 6, name: 'Michael'}
]
const uniqueData = [...data.reduce((map, obj) => map.set(obj.id, obj), new Map()).values()];
console.log(uniqueData)
/*
in `map.set(obj.id, obj)`
'obj.id' is key. (don't worry. we'll get only values using the .values() method)
'obj' is whole object.
*/
To add one more to the list. Using ES6 and Array.reduce with Array.find.
In this example filtering objects based on a guid property.
let filtered = array.reduce((accumulator, current) => {
if (! accumulator.find(({guid}) => guid === current.guid)) {
accumulator.push(current);
}
return accumulator;
}, []);
Extending this one to allow selection of a property and compress it into a one liner:
const uniqify = (array, key) => array.reduce((prev, curr) => prev.find(a => a[key] === curr[key]) ? prev : prev.push(curr) && prev, []);
To use it pass an array of objects and the name of the key you wish to de-dupe on as a string value:
const result = uniqify(myArrayOfObjects, 'guid')
Considering lodash.uniqWith
const objects = [{ 'x': 1, 'y': 2 }, { 'x': 2, 'y': 1 }, { 'x': 1, 'y': 2 }];
_.uniqWith(objects, _.isEqual);
// => [{ 'x': 1, 'y': 2 }, { 'x': 2, 'y': 1 }]
You could also use a Map:
const dedupThings = Array.from(things.thing.reduce((m, t) => m.set(t.place, t), new Map()).values());
Full sample:
const things = new Object();
things.thing = new Array();
things.thing.push({place:"here",name:"stuff"});
things.thing.push({place:"there",name:"morestuff"});
things.thing.push({place:"there",name:"morestuff"});
const dedupThings = Array.from(things.thing.reduce((m, t) => m.set(t.place, t), new Map()).values());
console.log(JSON.stringify(dedupThings, null, 4));
Result:
[
{
"place": "here",
"name": "stuff"
},
{
"place": "there",
"name": "morestuff"
}
]
Dang, kids, let's crush this thing down, why don't we?
let uniqIds = {}, source = [{id:'a'},{id:'b'},{id:'c'},{id:'b'},{id:'a'},{id:'d'}];
let filtered = source.filter(obj => !uniqIds[obj.id] && (uniqIds[obj.id] = true));
console.log(filtered);
// EXPECTED: [{id:'a'},{id:'b'},{id:'c'},{id:'d'}];
let myData = [{place:"here",name:"stuff"},
{place:"there",name:"morestuff"},
{place:"there",name:"morestuff"}];
let q = [...new Map(myData.map(obj => [JSON.stringify(obj), obj])).values()];
console.log(q)
One-liner using ES6 and new Map().
// assign things.thing to myData
let myData = things.thing;
[...new Map(myData.map(obj => [JSON.stringify(obj), obj])).values()];
Details:-
Doing .map() on the data list and converting each individual object into a [key, value] pair array(length =2), the first element(key) would be the stringified version of the object and second(value) would be an object itself.
Adding above created array list to new Map() would have the key as stringified object and any same key addition would result in overriding the already existing key.
Using .values() would give MapIterator with all values in a Map (obj in our case)
Finally, spread ... operator to give new Array with values from the above step.
A TypeScript solution
This will remove duplicate objects and also preserve the types of the objects.
function removeDuplicateObjects(array: any[]) {
return [...new Set(array.map(s => JSON.stringify(s)))]
.map(s => JSON.parse(s));
}
const things = [
{place:"here",name:"stuff"},
{place:"there",name:"morestuff"},
{place:"there",name:"morestuff"}
];
const filteredArr = things.reduce((thing, current) => {
const x = thing.find(item => item.place === current.place);
if (!x) {
return thing.concat([current]);
} else {
return thing;
}
}, []);
console.log(filteredArr)
Solution Via Set Object | According to the data type
const seen = new Set();
const things = [
{place:"here",name:"stuff"},
{place:"there",name:"morestuff"},
{place:"there",name:"morestuff"}
];
const filteredArr = things.filter(el => {
const duplicate = seen.has(el.place);
seen.add(el.place);
return !duplicate;
});
console.log(filteredArr)
Set Object Feature
Each value in the Set Object has to be unique, the value equality will be checked
The Purpose of Set object storing unique values according to the Data type , whether primitive values or object references.it has very useful four Instance methods add, clear , has & delete.
Unique & data Type feature:..
addmethod
it's push unique data into collection by default also preserve data type .. that means it prevent to push duplicate item into collection also it will check data type by default...
has method
sometime needs to check data item exist into the collection and . it's handy method for the collection to cheek unique id or item and data type..
delete method
it will remove specific item from the collection by identifying data type..
clear method
it will remove all collection items from one specific variable and set as empty object
Set object has also Iteration methods & more feature..
Better Read from Here : Set - JavaScript | MDN
removeDuplicates() takes in an array of objects and returns a new array without any duplicate objects (based on the id property).
const allTests = [
{name: 'Test1', id: '1'},
{name: 'Test3', id: '3'},
{name: 'Test2', id: '2'},
{name: 'Test2', id: '2'},
{name: 'Test3', id: '3'}
];
function removeDuplicates(array) {
let uniq = {};
return array.filter(obj => !uniq[obj.id] && (uniq[obj.id] = true))
}
removeDuplicates(allTests);
Expected outcome:
[
{name: 'Test1', id: '1'},
{name: 'Test3', id: '3'},
{name: 'Test2', id: '2'}
];
First, we set the value of variable uniq to an empty object.
Next, we filter through the array of objects. Filter creates a new array with all elements that pass the test implemented by the provided function.
return array.filter(obj => !uniq[obj.id] && (uniq[obj.id] = true));
Above, we use the short-circuiting functionality of &&. If the left side of the && evaluates to true, then it returns the value on the right of the &&. If the left side is false, it returns what is on the left side of the &&.
For each object(obj) we check uniq for a property named the value of obj.id (In this case, on the first iteration it would check for the property '1'.) We want the opposite of what it returns (either true or false) which is why we use the ! in !uniq[obj.id]. If uniq has the id property already, it returns true which evaluates to false (!) telling the filter function NOT to add that obj. However, if it does not find the obj.id property, it returns false which then evaluates to true (!) and returns everything to the right of the &&, or (uniq[obj.id] = true). This is a truthy value, telling the filter method to add that obj to the returned array, and it also adds the property {1: true} to uniq. This ensures that any other obj instance with that same id will not be added again.
Fast (less runtime) and type-safe answer for lazy Typescript developers:
export const uniqueBy = <T>( uniqueKey: keyof T, objects: T[]): T[] => {
const ids = objects.map(object => object[uniqueKey]);
return objects.filter((object, index) => !ids.includes(object[uniqueKey], index + 1));
}
This way works well for me:
function arrayUnique(arr, uniqueKey) {
const flagList = new Set()
return arr.filter(function(item) {
if (!flagList.has(item[uniqueKey])) {
flagList.add(item[uniqueKey])
return true
}
})
}
const data = [
{
name: 'Kyle',
occupation: 'Fashion Designer'
},
{
name: 'Kyle',
occupation: 'Fashion Designer'
},
{
name: 'Emily',
occupation: 'Web Designer'
},
{
name: 'Melissa',
occupation: 'Fashion Designer'
},
{
name: 'Tom',
occupation: 'Web Developer'
},
{
name: 'Tom',
occupation: 'Web Developer'
}
]
console.table(arrayUnique(data, 'name'))// work well
printout
┌─────────┬───────────┬────────────────────┐
│ (index) │ name │ occupation │
├─────────┼───────────┼────────────────────┤
│ 0 │ 'Kyle' │ 'Fashion Designer' │
│ 1 │ 'Emily' │ 'Web Designer' │
│ 2 │ 'Melissa' │ 'Fashion Designer' │
│ 3 │ 'Tom' │ 'Web Developer' │
└─────────┴───────────┴────────────────────┘
ES5:
function arrayUnique(arr, uniqueKey) {
const flagList = []
return arr.filter(function(item) {
if (flagList.indexOf(item[uniqueKey]) === -1) {
flagList.push(item[uniqueKey])
return true
}
})
}
These two ways are simpler and more understandable.
Here is a solution for ES6 where you only want to keep the last item. This solution is functional and Airbnb style compliant.
const things = {
thing: [
{ place: 'here', name: 'stuff' },
{ place: 'there', name: 'morestuff1' },
{ place: 'there', name: 'morestuff2' },
],
};
const removeDuplicates = (array, key) => {
return array.reduce((arr, item) => {
const removed = arr.filter(i => i[key] !== item[key]);
return [...removed, item];
}, []);
};
console.log(removeDuplicates(things.thing, 'place'));
// > [{ place: 'here', name: 'stuff' }, { place: 'there', name: 'morestuff2' }]
I know there is a ton of answers in this question already, but bear with me...
Some of the objects in your array may have additional properties that you are not interested in, or you simply want to find the unique objects considering only a subset of the properties.
Consider the array below. Say you want to find the unique objects in this array considering only propOne and propTwo, and ignore any other properties that may be there.
The expected result should include only the first and last objects. So here goes the code:
const array = [{
propOne: 'a',
propTwo: 'b',
propThree: 'I have no part in this...'
},
{
propOne: 'a',
propTwo: 'b',
someOtherProperty: 'no one cares about this...'
},
{
propOne: 'x',
propTwo: 'y',
yetAnotherJunk: 'I am valueless really',
noOneHasThis: 'I have something no one has'
}];
const uniques = [...new Set(
array.map(x => JSON.stringify(((o) => ({
propOne: o.propOne,
propTwo: o.propTwo
}))(x))))
].map(JSON.parse);
console.log(uniques);
Another option would be to create a custom indexOf function, which compares the values of your chosen property for each object and wrap this in a reduce function.
var uniq = redundant_array.reduce(function(a,b){
function indexOfProperty (a, b){
for (var i=0;i<a.length;i++){
if(a[i].property == b.property){
return i;
}
}
return -1;
}
if (indexOfProperty(a,b) < 0 ) a.push(b);
return a;
},[]);
Here I found a simple solution for removing duplicates from an array of objects using reduce method. I am filtering elements based on the position key of an object
const med = [
{name: 'name1', position: 'left'},
{name: 'name2', position: 'right'},
{name: 'name3', position: 'left'},
{name: 'name4', position: 'right'},
{name: 'name5', position: 'left'},
{name: 'name6', position: 'left1'}
]
const arr = [];
med.reduce((acc, curr) => {
if(acc.indexOf(curr.position) === -1) {
acc.push(curr.position);
arr.push(curr);
}
return acc;
}, [])
console.log(arr)
If array contains objects, then you can use this to remove duplicate
const persons= [
{ id: 1, name: 'John',phone:'23' },
{ id: 2, name: 'Jane',phone:'23'},
{ id: 1, name: 'Johnny',phone:'56' },
{ id: 4, name: 'Alice',phone:'67' },
];
const unique = [...new Map(persons.map((m) => [m.id, m])).values()];
if remove duplicates on the basis of phone, just replace m.id with m.phone
const unique = [...new Map(persons.map((m) => [m.phone, m])).values()];
Suppose I want to loop through an array of characters and build up an object which represents the frequency of each character, for example:
const frequency = {};
const str = 'stackoverflow';
for (let i = 0; i < str.length; i++) {
frequency[str[i]] = (frequency[str[i]] + 1) || 1;
}
With the above, we would expect an object in the form of:
{
s: 1,
t: 1,
a: 1,
c: 1,
k: 1,
o: 2,
v: 1,
e: 1,
r: 1,
f: 1,
l: 1,
w: 1
}
Now suppose I wanted to loop through an array of nested arrays, each with a form of [id, val]. Can I create an object such that I would end up with multiple keys, each representing a different id, and a corresponding array, filled with the values, in the same shorthand form as above?
For example:
[ [1,2], [1,3], [1,5], [2,7], [3,0], [1,10] ]
{
1: [2,3,5,10],
2: [7],
3: [0]
}
Is there something similar to:
const map = {};
for (let i = 0; i < list.length; i++) {
map[list[i][0]] = (map[list[i][0].push(map[list[i][1])) || [list[i][1]];
}
Functional approach with .reduce():
const list = [[1,2],[1,3],[1,5],[2,7],[3,0],[1,10]]
const x = list.reduce((a, [k, v]) => (a[k] = [...a[k] || [], v], a), {})
console.log(x)
Edit: stole #jered's much better conditional instead of ternary
Classic use case for a reducer:
const arr = [ [1,2], [1,3], [1,5], [2,7], [3,0], [1,10] ];
const map = arr.reduce((acc, cur) => {
return {
...acc,
[cur[0]]: [...(acc[cur[0]] || []), cur[1]]
};
}, {});
Of course, it could be a lot more readable than this... but computed property names and the spread syntax make it pretty slick and compact (it'd fit on a single line if you wanted to).
Edit: ooo I like #woat's use of single character var names and destructuring assignment in the function signature :) We could throw that in too:
const arr = [ [1,2], [1,3], [1,5], [2,7], [3,0], [1,10] ];
const map = arr.reduce((a, [k, v]) => ({...a, [k]: [...(a[k] || []), v]}), {});
const list = [ [1,2], [1,3], [1,5], [2,7], [3,0], [1,10] ];
const map = {};
for (let item of list) {
map[item[0]] = [...map[item[0]] || [], item[1]];
}
console.log(map);
I am learning about recursion at the moment and have moved on from numbers, string and arrays into using it on objects... I'm trying to work out the best method for taking an object as an argument and collecting the keys of the object and all nested objects into an array
I can return the object keys of a single object not using recursion. So i was trying to create a variable as an empty array then iterate over the object using a for loop and if "i" is an object then push object keys into the array variable and return it. This wouldnt work unfortunate.
I would like the following:
{lamp: 2, candle: 2, pillow: {big: 2, small: 4}, bathroom: {toilet: 1, shower: {shampoo: 1, conditioner: 2}}}
To return:
[lamp, candle, pillow, big, small, bathroom, toilet, shower, shampoo, conditioner]
Hope this explains enough, let me know if not :)
I tried the following:
function(obj) {
let keysArray = [];
for (let i = 0, i < obj.length, i++)
if (obj[i] === typeOf object) {
keysArray.push(obj[i].keys);
}
return keysArray
}
You can write a recursive function as follows
let obj = {lamp: 2, candle: 2, pillow: {big: 2, small: 4}, bathroom: {toilet: 1, shower: {shampoo: 1, conditioner: 2}}};
function getKeys(o) {
let result = [];
for (let key in o) {
result.push(key);
if(o[key] && typeof o[key] === "object") result.push(...getKeys(o[key]));
}
return result;
}
console.log(getKeys(obj));
You need to loop through the object using for...in. The for loop is for arrays
obj[i] === typeOf object is not correct. It should be typeof obj[key] === "object".
If the nested property is an object, you need to recursively call the function and push keys to keysArray
function getKeys(obj) {
let keysArray = [];
for (let key in obj) {
keysArray.push(key);
if (typeof obj[key] === "object")
keysArray.push(...getKeys(obj[key]))
}
return keysArray
}
const input={lamp:2,candle:2,pillow:{big:2,small:4},bathroom:{toilet:1,shower:{shampoo:1,conditioner:2}}}
console.log(getKeys(input))
FYI: typeof null is "object". So, the above code will throw an error if any of the properties are null. So, Object(obj[k]) === obj[k] can be used. This is true for all objects EXCEPT for null
Also, if flatMap is supported, you could do something like this
const input={lamp:2,candle:2,pillow:{big:2,small:4},bathroom:{toilet:1,shower:{shampoo:1,conditioner:2}}};
const getKeys = obj =>
Object.keys(obj).flatMap(key => Object(obj[key]) === obj[key]
? [key, ...getKeys(obj[key])]
: key)
console.log(getKeys(input))
How about:
const keys = obj => Object.keys(obj).reduce((acc, key) => {
acc.push(key);
return (obj[key] !== null && typeof obj[key] === 'object') // Avoid evaluating null as an object
? acc.concat(keys(obj[key]))
: acc;
}, []);
Usage:
keys({foo: 1, bar: {foobar: 2}}); // Outputs ['foo', 'bar', 'foobar']
A very good use-case for generators. Here's a demonstration -
const data =
{lamp: 2, candle: 2, pillow: {big: 2, small: 4}, bathroom: {toilet: 1, shower: {shampoo: 1, conditioner: 2}}}
const keys = function* (o = {}) {
if (Object(o) === o)
for (const [k, v] of Object.entries(o)) {
yield k
yield* keys(v)
}
}
console.log(Array.from(keys(data)))
// [lamp, candle, pillow, big, small, bathroom, toilet, shower, shampoo, conditioner]
Another solution is to use Array.prototype.flatMap -
const data =
{lamp: 2, candle: 2, pillow: {big: 2, small: 4}, bathroom: {toilet: 1, shower: {shampoo: 1, conditioner: 2}}}
const keys = (o = {}) =>
Object(o) === o
? Object.entries(o).flatMap(([ k, v ]) =>
[ k, ...keys(v) ]
)
: []
console.log(keys(data))
// [lamp, candle, pillow, big, small, bathroom, toilet, shower, shampoo, conditioner]
How can I transform a big object to array with lodash?
var obj = {
22: {name:"John", id:22, friends:[5,31,55], works:{books:[], films:[],}
12: {name:"Ivan", id:12, friends:[2,44,12], works:{books:[], films:[],}
}
// transform to
var arr = [{name:"John", id:22...},{name:"Ivan", id:12...}]
You can do
var arr = _.values(obj);
For documentation see here.
A modern native solution if anyone is interested:
const arr = Object.keys(obj).map(key => ({ key, value: obj[key] }));
or (not IE):
const arr = Object.entries(obj).map(([key, value]) => ({ key, value }));
_.toArray(obj);
Outputs as:
[
{
"name": "Ivan",
"id": 12,
"friends": [
2,
44,
12
],
"works": {
"books": [],
"films": []
}
},
{
"name": "John",
"id": 22,
"friends": [
5,
31,
55
],
"works": {
"books": [],
"films": []
}
}
]"
For me, this worked:
_.map(_.toPairs(data), d => _.fromPairs([d]));
It turns
{"a":"b", "c":"d", "e":"f"}
into
[{"a":"b"}, {"c":"d"}, {"e":"f"}]
There are quite a few ways to get the result you are after. Lets break them in categories:
ES6 Values only:
Main method for this is Object.values. But using Object.keys and Array.map you could as well get to the expected result:
Object.values(obj)
Object.keys(obj).map(k => obj[k])
var obj = {
A: {
name: "John"
},
B: {
name: "Ivan"
}
}
console.log('Object.values:', Object.values(obj))
console.log('Object.keys:', Object.keys(obj).map(k => obj[k]))
ES6 Key & Value:
Using map and ES6 dynamic/computed properties and destructuring you can retain the key and return an object from the map.
Object.keys(obj).map(k => ({[k]: obj[k]}))
Object.entries(obj).map(([k,v]) => ({[k]:v}))
var obj = {
A: {
name: "John"
},
B: {
name: "Ivan"
}
}
console.log('Object.keys:', Object.keys(obj).map(k => ({
[k]: obj[k]
})))
console.log('Object.entries:', Object.entries(obj).map(([k, v]) => ({
[k]: v
})))
Lodash Values only:
The method designed for this is _.values however there are "shortcuts" like _.map and the utility method _.toArray which would also return an array containing only the values from the object. You could also _.map though the _.keys and get the values from the object by using the obj[key] notation.
Note: _.map when passed an object would use its baseMap handler which is basically forEach on the object properties.
_.values(obj)
_.map(obj)
_.toArray(obj)
_.map(_.keys(obj), k => obj[k])
var obj = {
A: {
name: "John"
},
B: {
name: "Ivan"
}
}
console.log('values:', _.values(obj))
console.log('map:', _.map(obj))
console.log('toArray:', _.toArray(obj))
console.log('keys:', _.map(_.keys(obj), k => obj[k]))
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.min.js"></script>
Lodash Key & Value:
// Outputs an array with [[KEY, VALUE]]
_.entries(obj)
_.toPairs(obj)
// Outputs array with objects containing the keys and values
_.map(_.entries(obj), ([k,v]) => ({[k]:v}))
_.map(_.keys(obj), k => ({[k]: obj[k]}))
_.transform(obj, (r,c,k) => r.push({[k]:c}), [])
_.reduce(obj, (r,c,k) => (r.push({[k]:c}), r), [])
var obj = {
A: {
name: "John"
},
B: {
name: "Ivan"
}
}
// Outputs an array with [KEY, VALUE]
console.log('entries:', _.entries(obj))
console.log('toPairs:', _.toPairs(obj))
// Outputs array with objects containing the keys and values
console.log('entries:', _.map(_.entries(obj), ([k, v]) => ({
[k]: v
})))
console.log('keys:', _.map(_.keys(obj), k => ({
[k]: obj[k]
})))
console.log('transform:', _.transform(obj, (r, c, k) => r.push({
[k]: c
}), []))
console.log('reduce:', _.reduce(obj, (r, c, k) => (r.push({
[k]: c
}), r), []))
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.min.js"></script>
Note that in the above examples ES6 is used (arrow functions and dynamic properties).
You can use lodash _.fromPairs and other methods to compose an object if ES6 is an issue.
If you want the key (id in this case) to be a preserved as a property of each array item you can do
const arr = _(obj) //wrap object so that you can chain lodash methods
.mapValues((value, id)=>_.merge({}, value, {id})) //attach id to object
.values() //get the values of the result
.value() //unwrap array of objects
Transforming object to array with plain JavaScript's(ECMAScript-2016) Object.values:
var obj = {
22: {name:"John", id:22, friends:[5,31,55], works:{books:[], films:[]}},
12: {name:"Ivan", id:12, friends:[2,44,12], works:{books:[], films:[]}}
}
var values = Object.values(obj)
console.log(values);
If you also want to keep the keys use Object.entries and Array#map like this:
var obj = {
22: {name:"John", id:22, friends:[5,31,55], works:{books:[], films:[]}},
12: {name:"Ivan", id:12, friends:[2,44,12], works:{books:[], films:[]}}
}
var values = Object.entries(obj).map(([k, v]) => ({[k]: v}))
console.log(values);
Object to Array
Of all the answers I think this one is the best:
let arr = Object.entries(obj).map(([key, val]) => ({ key, ...val }))
that transforms:
{
a: { p: 1, q: 2},
b: { p: 3, q: 4}
}
to:
[
{ key: 'a', p: 1, q: 2 },
{ key: 'b', p: 3, q: 4 }
]
Array to Object
To transform back:
let obj = arr.reduce((obj, { key, ...val }) => { obj[key] = { ...val }; return obj; }, {})
To transform back keeping the key in the value:
let obj = arr.reduce((obj, { key, ...val }) => { obj[key] = { key, ...val }; return obj; }, {})
Will give:
{
a: { key: 'a', p: 1, q: 2 },
b: { key: 'b', p: 3, q: 4 }
}
For the last example you can also use lodash _.keyBy(arr, 'key') or _.keyBy(arr, i => i.key).
2017 update: Object.values, lodash values and toArray do it. And to preserve keys map and spread operator play nice:
// import { toArray, map } from 'lodash'
const map = _.map
const input = {
key: {
value: 'value'
}
}
const output = map(input, (value, key) => ({
key,
...value
}))
console.log(output)
// >> [{key: 'key', value: 'value'}])
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.js"></script>
var arr = _.map(obj)
You can use _.map function (of both lodash and underscore) with object as well, it will internally handle that case, iterate over each value and key with your iteratee, and finally return an array. Infact, you can use it without any iteratee (just _.map(obj)) if you just want a array of values. The good part is that, if you need any transformation in between, you can do it in one go.
Example:
var obj = {
key1: {id: 1, name: 'A'},
key2: {id: 2, name: 'B'},
key3: {id: 3, name: 'C'}
};
var array1 = _.map(obj, v=>v);
console.log('Array 1: ', array1);
/*Actually you don't need the callback v=>v if you
are not transforming anything in between, v=>v is default*/
//SO simply you can use
var array2 = _.map(obj);
console.log('Array 2: ', array2);
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.js"></script>
However, if you want to transform your object you can do so, even if you need to preserve the key, you can do that ( _.map(obj, (v, k) => {...}) with additional argument in map and then use it how you want.
However there are other Vanilla JS solution to this (as every lodash solution there should pure JS version of it) like:
Object.keys and then map them to values
Object.values (in ES-2017)
Object.entries and then map each key/value pairs (in ES-2017)
for...in loop and use each keys for feting values
And a lot more. But since this question is for lodash (and assuming someone already using it) then you don't need to think a lot about version, support of methods and error handling if those are not found.
There are other lodash solutions like _.values (more readable for specific perpose), or getting pairs and then map and so on. but in the case your code need flexibility that you can update it in future as you need to preserve keys or transforming values a bit, then the best solution is to use a single _.map as addresed in this answer. That will bt not that difficult as per readability also.
If you want some custom mapping (like original Array.prototype.map) of Object into an Array, you can just use _.forEach:
let myObject = {
key1: "value1",
key2: "value2",
// ...
};
let myNewArray = [];
_.forEach(myObject, (value, key) => {
myNewArray.push({
someNewKey: key,
someNewValue: value.toUpperCase() // just an example of new value based on original value
});
});
// myNewArray => [{ someNewKey: key1, someNewValue: 'VALUE1' }, ... ];
See lodash doc of _.forEach https://lodash.com/docs/#forEach