I have an array containing objects that every element but the last one are objects, but I want to convert them into an array of arrays and add the last element.
To be more explicit here is how I have it:
[
{ 0: [1,2], 1: [6,2], name: "" },
{ 0: [3,4], 1: [2,2], name: "" }
]
and the result I want is this one:
[
{ multipolygon: [ [1,2], [6,2] ], name: ""},
{ multipolygon: [ [3,4], [2,2] ], name: ""}
]
Each single array contained inside the original array is converted into an array of those arrays.
I have tried doing this:
const zonesArray = zones.map(el => Object.values(el)) // obj => array
const polygons = zonesArray.filter(el => el.pop()) // array without name
to get all the arrays contained inside the obj but then I realized how can I replace this into the original objects.
I have tried to modify the groupBy function found on MDN:
function groupBy(objectArray, property) {
return objectArray.reduce(function (acc, obj) {
let key = obj[property]
if (!acc[key]) {
acc[key] = []
}
acc[key].push(obj)
return acc
}, {})
}
But I can't seem to find the answer
It doesn't look like you're trying to group by a property, you're trying to transform each object in the array separately - which can be done by taking the name and the numeric properties together when mapping, then returning the shape of the new object:
const arr = [
{ 0: [1,2], 1: [6,2], name: "" },
{ 0: [3,4], 1: [2,2], name: "" }
];
const result = arr.map(({ name, ...rest }) => ({
name,
multipolygon: Object.values(rest)
}));
console.log(result);
Related
Are the steps I'm taking to solve this problem correct?
I'm working on turning a data structure of an array of arrays such as
this.arrayofAnimalsAndValues = [
[ "Ant", 1287, 12956],
[ "Lion", 2574, 25826],
[ "Bear", 3861, 38696],
.....
]
into this
this.jsonOfAnimalsAndValues = [
{category: "Ant", value_1: 1287, value_2:12956},
{category: "Lion", value_1: 2574, value_2:25826},
{category: "Bear", value_1: 3861, value_2:38696},
.....
]
where the first item in the array is always assigned to 'category' in the array object and the following items assigned to value_# depending on their order in the array. So the 2nd array item would have key value_1 and so on. For example, for 1 nested array:
[[ "Ant", 5148, 51566]] to =>
[{category: "Ant", value_1: "5148", value_2: 51566}]
I've created a hardcoded way to achieve this however I'm trying to make it dynamic:
'hardcoded' way:
this.variableOfKeys = ["value_1", "value_2", "value_3", ......]
this.jsonOfAnimalsAndValues = this.arrayofAnimalsAndValues(function(x) {
return {
category: x[0],
no1: x[1],
no2: x[2],
.....
};
});
where I just hardcode the keys and their values (values using their index).
My attempt to make it dynamic:
this.variableOfKeys.forEach(element => {
this.jsonOfAnimalsAndValues = this.arrayofAnimalsAndValues.map(function(x) {
for (var i = 0; i<=this.arrayOfValuesToUseAsKeys.length; ++i) {
return {
category: x[0],
element: x[i+1],
};
}
});
});
where my logic is that for each item in
this.variableOfKeys = ["value_1", "value_2", "value_3", ......],
I created this.jsonOfAnimalsAndValues such that the first item (item with the 0th index) in the array this.arrayofAnimalsAndValues is assigned to the key category and the following items (depending on their index) are assigned to the values in this.variableOfKeys in order starting from no1, then no2 etc.
However, I don't think this is written correctly and I keep getting this error:
"TypeError: Cannot read property 'variableOfKeys' of undefined"
Can I ask how it might be written incorrectly and so how I might be able to create this.jsonOfAnimalsAndValues from this.arrayofAnimalsAndValues?
You can map each subarray to an array of entries, then turn it into an object to return with Object.fromEntries:
const arrayofAnimalsAndValues = [
[ "Ant", 1287, 12956],
[ "Lion", 2574, 25826],
[ "Bear", 3861, 38696],
];
const output = arrayofAnimalsAndValues.map(
([category, ...rest]) => Object.fromEntries([
['category', category],
...rest.map((value, i) => ['value_' + (i + 1), value])
])
);
console.log(output);
Given an array of the keys you can map() the main array and use reduce() on each subarray to generate each object
const arr=[["Ant",1287,12956],["Lion",2574,25826],["Bear",3861,38696]],
keys = ['category','value_1','value_2'];
const res = arr.map(e => e.reduce((a,c,i) => (a[keys[i]] = c, a),{}))
console.log(res)
.as-console-wrapper { max-height: 100%!important;top:0}
I've got two arrays that have multiple objects
[
{
"name":"paul",
"employee_id":"8"
}
]
[
{
"years_at_school": 6,
"department":"Mathematics",
"e_id":"8"
}
]
How can I achieve the following with either ES6 or Lodash?
[
{
"name":"paul",
"employee_id":"8"
"data": {
"years_at_school": 6
"department":"Mathematics",
"e_id":"8"
}
}
]
I can merge but I'm not sure how to create a new child object and merge that in.
Code I've tried:
school_data = _.map(array1, function(obj) {
return _.merge(obj, _.find(array2, {employee_id: obj.e_id}))
})
This merges to a top level array like so (which is not what I want):
{
"name":"paul",
"employee_id":"8"
"years_at_school": 6
"department":"Mathematics",
"e_id":"8"
}
The connector between these two is "employee_id" and "e_id".
It's imperative that it's taken into account that they could be 1000 objects in each array, and that the only way to match these objects up is by "employee_id" and "e_id".
In order to match up employee_id and e_id you should iterate through the first array and create an object keyed to employee_id. Then you can iterate though the second array and add the data to the particular id in question. Here's an example with an extra item added to each array:
let arr1 = [
{
"name":"mark",
"employee_id":"6"
},
{
"name":"paul",
"employee_id":"8"
}
]
let arr2 = [
{
"years_at_school": 6,
"department":"Mathematics",
"e_id":"8"
},
{
"years_at_school": 12,
"department":"Arr",
"e_id":"6"
}
]
// empObj will be keyed to item.employee_id
let empObj = arr1.reduce((obj, item) => {
obj[item.employee_id] = item
return obj
}, {})
// now lookup up id and add data for each object in arr2
arr2.forEach(item=>
empObj[item.e_id].data = item
)
// The values of the object will be an array of your data
let merged = Object.values(empObj)
console.log(merged)
If you perform two nested O(n) loops (map+find), you'll end up with O(n^2) performance. A typical alternative is to create intermediate indexed structures so the whole thing is O(n). A functional approach with lodash:
const _ = require('lodash');
const dataByEmployeeId = _(array2).keyBy('e_id');
const result = array1.map(o => ({...o, data: dataByEmployeeId.get(o.employee_id)}));
Hope this help you:
var mainData = [{
name: "paul",
employee_id: "8"
}];
var secondaryData = [{
years_at_school: 6,
department: "Mathematics",
e_id: "8"
}];
var finalData = mainData.map(function(person, index) {
person.data = secondaryData[index];
return person;
});
Sorry, I've also fixed a missing coma in the second object and changed some other stuff.
With latest Ecmascript versions:
const mainData = [{
name: "paul",
employee_id: "8"
}];
const secondaryData = [{
years_at_school: 6,
department: "Mathematics",
e_id: "8"
}];
// Be careful with spread operator over objects.. it lacks of browser support yet! ..but works fine on latest Chrome version for example (69.0)
const finalData = mainData.map((person, index) => ({ ...person, data: secondaryData[index] }));
Your question suggests that both arrays will always have the same size. It also suggests that you want to put the contents of array2 within the field data of the elements with the same index in array1. If those assumptions are correct, then:
// Array that will receive the extra data
const teachers = [
{ name: "Paul", employee_id: 8 },
{ name: "Mariah", employee_id: 10 }
];
// Array with the additional data
const extraData = [
{ years_at_school: 6, department: "Mathematics", e_id: 8 },
{ years_at_school: 8, department: "Biology", e_id: 10 },
];
// Array.map will iterate through all indices, and gives both the
const merged = teachers.map((teacher, index) => Object.assign({ data: extraData[index] }, teacher));
However, if you want the data to be added to the employee with an "id" matching in both arrays, you need to do the following:
// Create a function to obtain the employee from an ID
const findEmployee = id => extraData.filter(entry => entry.e_id == id);
merged = teachers.map(teacher => {
const employeeData = findEmployee(teacher.employee_id);
if (employeeData.length === 0) {
// Employee not found
throw new Error("Data inconsistency");
}
if (employeeData.length > 1) {
// More than one employee found
throw new Error("Data inconsistency");
}
return Object.assign({ data: employeeData[0] }, teacher);
});
A slightly different approach just using vanilla js map with a loop to match the employee ids and add the data from the second array to the matching object from the first array. My guess is that the answer from #MarkMeyer is probably faster.
const arr1 = [{ "name": "paul", "employee_id": "8" }];
const arr2 = [{ "years_at_school": 6, "department": "Mathematics", "e_id": "8" }];
const results = arr1.map((obj1) => {
for (const obj2 of arr2) {
if (obj2.e_id === obj1.employee_id) {
obj1.data = obj2;
break;
}
}
return obj1;
});
console.log(results);
I'm learning to manipulate JSON data and I am stuck trying to figure out how to cajole the following JSON into what I want as shown below:
Any pointers to function/terms/concepts that I should learn for this sort of problem would be greatly appreciated! Thanks
JSON object
{
car: 1,
van: 5,
cat: 99999999999999999999999
}
Desired outcome:
items: [
{ "type": "car", "value": "1"},
{ "type": "van", "value": "5"},
{ "type": "cat", "value": "99999999999999999999999"}
]
You can use a combination of Object.entries and Array.prototype.map:
const obj = { car: 1, van: 5, cat: 99999999999999999999999 };
let list = Object.entries(obj) // [["car",1],["van",5],["cat",99999999999999999999999]]
.map(x => ({ type: x[0], value: x[1] }));
console.log(list);
Or, with some destructuring:
const obj = { car: 1, van: 5, cat: 99999999999999999999999 };
let list = Object.entries(obj)
.map(([type, value]) => ({ type, value }));
console.log(list);
The callback to map:
([type, value]) => ({ type, value })
Expects an array as parameter: [type, value]. The first value in that array is assigned to type, the second one to value.
Then we use a shorthand form to set these values in our returned object:
=> ({ type, value })
I'm a beginner. I tried to solve the problem and this is the best I can come up with, tested in Node.js 10.
const obj = {"car": 1, "van": 5, "cat": 999999}
const items = []
for (let key in obj) {
items.push({"type": key, "value": obj[key]})
}
console.log(items)
One thing I am slightly confused about is the difference between for..in vs for..of, I'm currently looking into it.
Object.keys will return:
['car', 'van', 'cat'];
On this array you can use Array's map function which creates a new array with the results of calling a provided function on every element in the calling array.
var a = {
car: 1,
van: 5,
cat: 99999999999999999999999
}
m = Object.keys(a).map((v)=>{
return {
type: v,
value: a[v]
}
})
console.log(m);
#GustavMahler hope you understand. To learn more about array functions you should look map, reduce and filter.
This one uses object.keys
let js = {car:1, van:5, cat:9999}
Object.keys(js).map( x => ({type: x, value: js[x] }) )
[ { type: 'car', value: 1 },
{ type: 'van', value: 5 },
{ type: 'cat', value: 9999 } ]
This question already has answers here:
Find object by id in an array of JavaScript objects
(36 answers)
Closed 4 years ago.
I have an array of json objects:
[ {id:0, name:'A'}, {id:1, name:'B'}...{id:n, name:'N'} ]
How do i get the value (name) base on a given id, without iterating the array? Perhaps using map or some filter method...
const arr = [ {id:0, name:'A'}, {id:1, name:'B'},{id:3, name:'N'} ];
const inputId = 1;
const foundObj = arr.find(({ id }) => id === inputId);
if (foundObj) console.log(foundObj.name);
This still does iterate the array internally, though (as any method will).
This find method will find object based on your object property and value.
ArrayName.find(x => x.id === 0);
let array = [ {id:0, name:'A'}, {id:1, name:'B'}, {id:'n', name:'N'} ]
//To search in array we must iterate. But if you want to optimise performance for multiple searches you can map it to object by id.
let map = array.reduce((acc,element)=>{acc[element.id]=element;return acc;},{})
console.log(map[0])
console.log(map[1])
console.log(map.n) //As n was used as id.
Maps take one iteration to construct. Value retrieval thereon is sublinear.
// Input.
const input = [{id: 0, name:'A'}, {id: 1, name:'B'}, {id: 13, name:'N'}]
// To Map.
const toMap = (A) => new Map(A.map(x => [x.id, x]))
// Output.
const output = toMap(input)
// Proof.
console.log(output.get(0))
console.log(output.get(1))
console.log(output.get(13))
When you want to find an element in a collection, array might not be the best choice, objects or maps are much better in that case.
Each time you have to find an element, you would have to iterate over the array which would take O(n) time.
To avoid this, you could have an API layer in the middle, to convert your array into an a data structure which maps values by unique keys. You could achieve this by a plain Javascript Object.
That way you could find your element by id in O(1) without any iteration.
//original data
let arr = [ {id:0, name:'A'}, {id:1, name:'B'}, {id:2, name:'N'} ];
//convert it into object
let obj = arr.reduce((acc, curr) => {
acc[curr.id] = curr;
return acc;
}, {});
//modified data
{ 0: { id: 0, name: 'A' },
1: { id: 1, name: 'B' },
2: { id: 2, name: 'N' } }
//Now, you can look up value on any id as
obj[id].name;
This question already has answers here:
How to convert an array of objects to object with key value pairs
(7 answers)
How to convert an array of key-value tuples into an object
(14 answers)
Closed 5 years ago.
I would like to turn this:
let myArray = [ {city: "NY"}, {status: 'full'} ];
to this:
let myObj = { city: "NY", status: 'full' };
while I tried this:
let newObj = {};
for (var i = 0; i < myArray.length; i++) {
(function(x) {
newObj = Object.assign(myArray[i]);
})(i);
}
it assigns the last pair to the object
Spread the array into Object#assign:
const myArray = [ {city: "NY"}, {status: 'full'} ];
const myObj = Object.assign({}, ...myArray);
console.log(myObj);
Note: Assign into an empty object. If you omit the empty object, the 1st element of the original array will be mutated (everything will be merged into it).
You could also use Array.reduce() which will give you more fine grain control:
const myArray = [
{ city: 'NY', color: 'blue', rodents: { small: false, medium: false, large: true } },
{ status: 'full', color: 'red' },
{ sandwich: 'flavourful' },
]
// item is each object in your array
const reduced = myArray.reduce((newObj, item) => {
// existing props will be overwritten by newer object entries in the array
// this example is same as Object.assign spread with right to left precedence,
// until you want more custom logic
Object.keys(item).forEach((key) => { newObj[key] = item[key] })
return newObj
}, {})
console.log(reduced)
// you will see `red` overwrite `blue`
EDIT: after examining this answer after a year, I note that it isn't optimized at all for ability to deep clone or deep merge. I recommend studying those aspects closer and to be careful of copying or breaking references if you are working immutably.
There is no issue with this in the above example because all values are primitives.
I would tend to agree with Ori that your question seems to be about creating an indexed object which isn't usually a good plan, but if its necessary to key your object with numbers you can do it like this:
let newObj = {};
myArray.forEach((val, index) => { newObj[index] = val });
let myArray = [ {city: "NY"}, {status: 'full'} ];
let newObj = myArray.reduce((acc, curr) => {
Object.keys(curr).forEach(val => {
acc[val] = curr[val]
})
return acc
}, {})
console.log(newObj)
This syntax is supported in IE according to caniuse.com