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Is there a way to create object with common value as key and assigning the common objects as array values?

Let's say i have an array of four objects
var data = [
{a: 1, b: 2},
{a: 2, b: 4},
{a: 1, b: 6},
{a: 2, b: 9}
];
And i want to create an object say
Taking common value and passing it as key and assigning the value ob common objects to an array like below
Const treat = {
1:[{a:1,b:2} {a:1,b:6}],
2:[{a:2,b:4} {a:2,b:9}]
}

Here is a version of what you want. You can research different array methods such as reduce to see other ways to obtain similar results.
var data = [{
a: 1,
b: 2
},
{
a: 2,
b: 4
},
{
a: 1,
b: 6
},
{
a: 2,
b: 9
}
];
function sortData() {
var sortedData = {};
data.forEach(sample => {
// Need to check if the array for the sample has been created since we cannot "push" to "undefined".
if (sortedData[sample.a]) {
sortedData[sample.a].push(sample);
} else {
sortedData[sample.a] = [sample];
}
});
return sortedData;
}
console.log(sortData());

How do I search through every instance of a key and see if it matches a variable, and then execute an action if so? [duplicate]

This question already has answers here:
Find object by id in an array of JavaScript objects
(36 answers)
Closed 4 years ago.
Let's say I have an array of four objects:
var jsObjects = [
{a: 1, b: 2},
{a: 3, b: 4},
{a: 5, b: 6},
{a: 7, b: 8}
];
Is there a way that I can get the third object ({a: 5, b: 6}) by the value of the property b for example without a for...in loop?

Filter array of objects, which property matches value, returns array:
var result = jsObjects.filter(obj => {
return obj.b === 6
})
See the MDN Docs on Array.prototype.filter()
const jsObjects = [
{a: 1, b: 2},
{a: 3, b: 4},
{a: 5, b: 6},
{a: 7, b: 8}
]
let result = jsObjects.filter(obj => {
return obj.b === 6
})
console.log(result)
Find the value of the first element/object in the array, otherwise undefined is returned.
var result = jsObjects.find(obj => {
return obj.b === 6
})
See the MDN Docs on Array.prototype.find()
const jsObjects = [
{a: 1, b: 2},
{a: 3, b: 4},
{a: 5, b: 6},
{a: 7, b: 8}
]
let result = jsObjects.find(obj => {
return obj.b === 6
})
console.log(result)

jsObjects.find(x => x.b === 6)
From MDN:
The find() method returns a value in the array, if an element in the array satisfies the provided testing function. Otherwise undefined is returned.
Side note: methods like find() and arrow functions are not supported by older browsers (like IE), so if you want to support these browsers, you should transpile your code using Babel.

I don't know why you are against a for loop (presumably you meant a for loop, not specifically for..in), they are fast and easy to read. Anyhow, here's some options.
For loop:
function getByValue(arr, value) {
for (var i=0, iLen=arr.length; i<iLen; i++) {
if (arr[i].b == value) return arr[i];
}
}
.filter
function getByValue2(arr, value) {
var result = arr.filter(function(o){return o.b == value;} );
return result? result[0] : null; // or undefined
}
.forEach
function getByValue3(arr, value) {
var result = [];
arr.forEach(function(o){if (o.b == value) result.push(o);} );
return result? result[0] : null; // or undefined
}
If, on the other hand you really did mean for..in and want to find an object with any property with a value of 6, then you must use for..in unless you pass the names to check.
Example
function getByValue4(arr, value) {
var o;
for (var i=0, iLen=arr.length; i<iLen; i++) {
o = arr[i];
for (var p in o) {
if (o.hasOwnProperty(p) && o[p] == value) {
return o;
}
}
}
}

Ways to achieve the requirement :
Using Array.find() method :
const jsObject = [
{a: 1, b: 2},
{a: 3, b: 4},
{a: 5, b: 6},
{a: 7, b: 8}
];
const filteredResult = jsObject.find((e) => e.b == 6);
console.log(filteredResult);
Using Array.filter() method :
const jsObjects = [
{a: 1, b: 2},
{a: 3, b: 4},
{a: 5, b: 6},
{a: 7, b: 8}
];
const filterObj = jsObjects.filter((e) => e.b == 6);
console.log(filterObj[0]);
Using for...in loop :
const jsObjects = [
{a: 1, b: 2},
{a: 3, b: 4},
{a: 5, b: 6},
{a: 7, b: 8}
];
for (const i in jsObjects) {
if (jsObjects[i].b == 6) {
console.log(jsObjects[i]);
}
}

OK, there are few ways to do that, but let's start with the simplest one and latest approach to do this, this function is called find().
Just be careful when you using find to as even IE11 dosn't support it, so it needs to be transpiled...
so you have this object as you said:
var jsObjects = [
{a: 1, b: 2},
{a: 3, b: 4},
{a: 5, b: 6},
{a: 7, b: 8}
];
and you can write a function and get it like this:
function filterValue(obj, key, value) {
return obj.find(function(v){ return v[key] === value});
}
and use the function like this:
filterValue(jsObjects, "b", 6); //{a: 5, b: 6}
Also in ES6 for even shortened version:
const filterValue = (obj, key, value)=> obj.find(v => v[key] === value);
This method only return the first value which match..., for better result and browser support, you can use filter:
const filterValue = (obj, key, value)=> obj.filter(v => v[key] === value);
and we will return [{a: 5, b: 6}]...
This method will return an array instead...
You simpley use for loop as well, create a function like this:
function filteredArray(arr, key, value) {
const newArray = [];
for(i=0, l=arr.length; i<l; i++) {
if(arr[i][key] === value) {
newArray.push(arr[i]);
}
}
return newArray;
}
and call it like this:
filteredArray(jsObjects, "b", 6); //[{a: 5, b: 6}]

See this documentation Array.prototype.find()
Example:
var inventory = [
{name: 'apples', quantity: 2},
{name: 'bananas', quantity: 0},
{name: 'cherries', quantity: 5}
];
function findCherries(fruit) {
return fruit.name === 'cherries';
}
console.log(inventory.find(findCherries));
// { name: 'cherries', quantity: 5 }

Using underscore.js:
var foundObject = _.findWhere(jsObjects, {b: 6});

It looks like in the ECMAScript 6 proposal there are the Array methods find() and findIndex(). MDN also offers polyfills which you can include to get the functionality of these across all browsers.
find():
function isPrime(element, index, array) {
var start = 2;
while (start <= Math.sqrt(element)) {
if (element % start++ < 1) return false;
}
return (element > 1);
}
console.log( [4, 6, 8, 12].find(isPrime) ); // undefined, not found
console.log( [4, 5, 8, 12].find(isPrime) ); // 5
findIndex():
function isPrime(element, index, array) {
var start = 2;
while (start <= Math.sqrt(element)) {
if (element % start++ < 1) return false;
}
return (element > 1);
}
console.log( [4, 6, 8, 12].findIndex(isPrime) ); // -1, not found
console.log( [4, 6, 7, 12].findIndex(isPrime) ); // 2

If I understand correctly, you want to find the object in the array whose b property is 6?
var found;
jsObjects.some(function (obj) {
if (obj.b === 6) {
found = obj;
return true;
}
});
Or if you were using underscore:
var found = _.select(jsObjects, function (obj) {
return obj.b === 6;
});

If you are looking for a single result, rather than an array, may I suggest reduce?
Here is a solution in plain 'ole javascript that returns a matching object if one exists, or null if not.
var result = arr.reduce(function(prev, curr) { return (curr.b === 6) ? curr : prev; }, null);

You can use it with the arrow function as well like as below :
var demoArray = [
{name: 'apples', quantity: 2},
{name: 'bananas', quantity: 0},
{name: 'cherries', quantity: 5}
];
var result = demoArray.filter( obj => obj.name === 'apples')[0];
console.log(result);
// {name: 'apples', quantity: 2}

How about using _.find(collection, [predicate=_.identity], [fromIndex=0]) of lo-dash to get object from array of objects by object property value. You could do something like this:
var o = _.find(jsObjects, {'b': 6});
Arguments:
collection (Array|Object): The collection to inspect.
[predicate=_.identity] (Function): The function invoked per iteration.
[fromIndex=0] (number): The index to search from.
Returns
(*): Returns the matched element (in your case, {a: 5, b: 6}), else undefined.
In terms of performance, _.find() is faster as it only pulls the first object with property {'b': 6}, on the other hand, if suppose your array contains multiple objects with matching set of properties (key:value), then you should consider using _.filter() method. So in your case, as your array has a single object with this property, I would use _.find().

Made the best/fastest part of this answer more re-usable & clear:
function getElByPropVal(myArray, prop, val){
for (var i = 0, length = myArray.length; i < length; i++) {
if (myArray[i][prop] == val){
return myArray[i];
}
}
}

var result = jsObjects.filter(x=> x.b === 6);
will be better, using return in filter sometimes you can't get result (I dunno why)

To get first object from array of objects by a specific property value:
function getObjectFromObjectsArrayByPropertyValue(objectsArray, propertyName, propertyValue) {
return objectsArray.find(function (objectsArrayElement) {
return objectsArrayElement[propertyName] == propertyValue;
});
}
function findObject () {
var arrayOfObjectsString = document.getElementById("arrayOfObjects").value,
arrayOfObjects,
propertyName = document.getElementById("propertyName").value,
propertyValue = document.getElementById("propertyValue").value,
preview = document.getElementById("preview"),
searchingObject;
arrayOfObjects = JSON.parse(arrayOfObjectsString);
console.debug(arrayOfObjects);
if(arrayOfObjects && propertyName && propertyValue) {
searchingObject = getObjectFromObjectsArrayByPropertyValue(arrayOfObjects, propertyName, propertyValue);
if(searchingObject) {
preview.innerHTML = JSON.stringify(searchingObject, false, 2);
} else {
preview.innerHTML = "there is no object with property " + propertyName + " = " + propertyValue + " in your array of objects";
}
}
}
pre {
padding: 5px;
border-radius: 4px;
background: #f3f2f2;
}
textarea, button {
width: 100%
}
<fieldset>
<legend>Input Data:</legend>
<label>Put here your array of objects</label>
<textarea rows="7" id="arrayOfObjects">
[
{"a": 1, "b": 2},
{"a": 3, "b": 4},
{"a": 5, "b": 6},
{"a": 7, "b": 8, "c": 157}
]
</textarea>
<hr>
<label>property name: </label> <input type="text" id="propertyName" value="b"/>
<label>property value: </label> <input type="text" id="propertyValue" value=6 />
</fieldset>
<hr>
<button onclick="findObject()">find object in array!</button>
<hr>
<fieldset>
<legend>Searching Result:</legend>
<pre id="preview">click find</pre>
</fieldset>

Using find with bind to pass specific key values to a callback function.
function byValue(o) {
return o.a === this.a && o.b === this.b;
};
var result = jsObjects.find(byValue.bind({ a: 5, b: 6 }));

var jsObjects = [{a: 1, b: 2}, {a: 3, b: 4}, {a: 5, b: 6}, {a: 7, b: 8}];
to access the third object, use: jsObjects[2];
to access the third object b value, use: jsObjects[2].b;

How would you check if property name(s) from one object exist in another?

I am trying to transfer/copy properties from object1 to object2, but only properties that are undefined in object2.
Thanks in advance, I hope this comes across clearly!
let object1 = { a: 1, b: 2, c: 3, d: 4 }
let object2 = { a: 'string' }
fillObj = function (object2, object1) {
for (let key in object1) {
if (typeof object2.key === undefined) {
object2[key] = object1[key];
}
}
return object2; //should return {a: 'string', b: 2, c: 3, d: 4 }
};

(1) Look properties on an object by a variable property name by using bracket notation, not dot notation
(2) To check if something is undefined, either compare against undefined directly, or use typeof and compare against the string 'undefined' (but this check isn't needed for this algorithm)
(3) Make sure the properties are own properties, not inherited properties, with hasOwnProperty
let object1 = { a: 'string' }
let object2 = { a: 1, b: 2, c: 3, d: 4 }
fillObj = function (object2, object1) {
for (let key in object1) {
if (object1.hasOwnProperty(key)) {
object2[key] = object1[key];
}
}
return object2; //should return {a: 'string', b: 2, c: 3, d: 4 }
};
console.log(fillObj(object2, object1));
Or use Object.entries, which iterates over own-properties only:
let object1 = { a: 'string' }
let object2 = { a: 1, b: 2, c: 3, d: 4 }
fillObj = function (object2, object1) {
for (const [key, val] of Object.entries(object1)) {
object2[key] = val;
}
return object2; //should return {a: 'string', b: 2, c: 3, d: 4 }
};
console.log(fillObj(object2, object1));

How to change key name with map into nested object?

Here is the object
{
a: 1,
b: {
c: {
d: 2
},
e: 3
}
}
Here is the map
{
'a': 'aaa',
'b': 'bbb',
'b.c.d': 'bcd'
}
Here is the expected result.
{
aaa: 1,
bbb: {
c: {
bcd: 2
},
e: 3
}
}
I know there's a function in lodash _.get could get the value like b.c.d.
But how can I change the key name with the map?

You can do this recursively by keeping track of the current path and building a key into the map with that:
let o = {a: 1,b: {c: {d: 2},e: 3}}
let map = {
'a': 'aaa',
'b': 'bbb',
'b.c.d': 'bcd'
}
function makeObj(obj, map, p=[]) {
let ret = {}
Object.entries(obj).forEach(([k, v]) => {
let path = p.concat(k) // add onto current path
let mapKey = map[path.join('.')] || k
ret[mapKey] = (typeof v === 'object')
? makeObj(v, map, path) // if an object recurse and pass on the current path
: v // otherwise set the value
})
return ret
}
console.log(makeObj(o, map))

Access a property on an object from an array of keys

I want to write a helper function to unpack a specific object property from each object in an array of objects. Sometimes this property will be top level, other times it will be nested an arbitrary number of levels. So the crux of this question is: how can I access an object property based on an array of key names of variable length?
I'm hoping for something like:
const func = (arrOfObjects, ...keys) {
return arrOfObjects.map(object => {
return object[keys[0]][keys[1]] ... [keys[N]];
})
}
with example behaviour:
const input = [
{a: b: {c: 10}},
{a: b: {c: 11}},
{a: b: {c: 12}}
]
console.log(func(input, 'a', 'b', 'c'))
// [10, 11, 12]
console.log(func(input, 'a', 'b'))
// [{c: 10}, {c: 11}, {c : 12}]
I feel like there has to be a nice ES6 wizardry solution but as yet haven't found it so any help would be much appreciated!
Cheers,
P

You can get a short and easy solution using Array#reduce
const input = [
{a: { b: {c: 10}}},
{a: { b: {c: 11}}},
{a: { b: {c: 12}}}
]
console.log(func(input, ['a', 'b', 'c']))
// [10, 11, 12]
console.log(func(input, ['a', 'b']))
// [{c: 10}, {c: 11}, {c : 12}]
function func(input, props) {
return input.map(x => exctractByProps(x, props));
}
function exctractByProps(obj, props) {
return props.reduce(
(acc, prop) => typeof acc === 'object' && prop in acc ? acc[prop] : undefined,
obj
)
}
The main logic is to grab all the properties passed in and then try to get the value corresponding to obj[prop[0]][prop[1]][prop[2]]/* ... */[prop[n]]. If the object has an odd shape that doesn't match up with prop (for example, an input of {a: 1}, ['a', 'b'] or {d: {c: 1}}, ['a', 'b']) then the function returns undefined.

Based on the answers you gave me to my questions and your example. It seems as if the order will of the input will always match the objects nesting. So here is my solution:
const func = (arrOfObjects, ...keys) => {
return arrOfObjects.map(object => {
let obj = object, integer = keys.length;
for (let index = 0; index < integer; index++) {
obj = obj[keys[index]];
if(obj === undefined) break;
}
return obj;
});
};
const input = [
{ a: { b: { c: 10 } } },
{ a: { b: { c: 11 } } },
{ a: { b: { c: 12 } } }
];
console.log(func(input, "a", "b", "c"));
// [10, 11, 12]
console.log(func(input, "a", "b"));
// [{c: 10}, {c: 11}, {c : 12}]
Unfortunately there is no such thing as the javascript magic you where expecting.
Note: this code will not work when the order of the keys inside the object are nested at random depth. But for what you are trying to solve, this should work just fine. Also, I tried to preserve your initial code as good as possible

If you supply the accessor like [a, b, c[0], name], you can write a custom function which returns the value if found in a nested Object, otherwise returns undefined
let obj = {
a: 1,
b: 2,
c: {
d: 1,
e: [{
f: 3,
g: [{
z: 45
}]
}]
}
}
function findKeyFromPattern(obj, patternArr) {
let value = obj;
for(let i = 0; i < patternArr.length; i++) {
const arrmatch = patternArr[i].match(/(\w+)\[(\d+)\]/);
if(arrmatch) { // pattern matches and array accessor syntax
value = value[arrmatch[1]];
if(typeof value === 'object' && value !== null) {
value = value[arrmatch[2]];
} else {
return;
}
} else {
if(value[patternArr[i]]) {
value = value[patternArr[i]];
} else {
return;
}
}
}
return value;
}
console.log(findKeyFromPattern(obj, ['c', 'e[0]', 'g']));
console.log(findKeyFromPattern(obj, ['c', 'e[1]', 'g']))