What is the best way to convert:
['a','b','c']
to:
{
0: 'a',
1: 'b',
2: 'c'
}
_.keyBy
(formerly _.indexBy
): lodash.com/docs#keyBy
_.toPlainObject
. Ex: var myObj = _.toPlainObject(myArr)
ECMAScript 6 introduces the easily polyfillable Object.assign
:
The Object.assign() method is used to copy the values of all enumerable own properties from one or more source objects to a target object. It will return the target object.
Object.assign({}, ['a','b','c']); // {0:"a", 1:"b", 2:"c"}
The own length
property of the array is not copied because it isn't enumerable.
Also, you can use ES8 spread syntax on objects to achieve the same result:
{ ...['a', 'b', 'c'] }
For custom keys you can use reduce:
['a', 'b', 'c'].reduce((a, v) => ({ ...a, [v]: v}), {})
// { a: "a", b: "b", c: "c" }
With a function like this:
function toObject(arr) {
var rv = {};
for (var i = 0; i < arr.length; ++i)
rv[i] = arr[i];
return rv;
}
Your array already is more-or-less just an object, but arrays do have some "interesting" and special behavior with respect to integer-named properties. The above will give you a plain object.
edit oh also you might want to account for "holes" in the array:
function toObject(arr) {
var rv = {};
for (var i = 0; i < arr.length; ++i)
if (arr[i] !== undefined) rv[i] = arr[i];
return rv;
}
In modern JavaScript runtimes, you can use the .reduce()
method:
var obj = arr.reduce(function(acc, cur, i) {
acc[i] = cur;
return acc;
}, {});
That one also avoids "holes" in the array, because that's how .reduce()
works.
[]
) if you're not going to use numeric property keys and the "length" property.
const obj = arr.reduce((obj, cur, i) => { return { ...obj, [i]: cur }; }, {});
const obj = arr.reduce((obj, cur, i) => ({ ...obj, [i]: cur }), {});
arr.reduce((obj, cur, i) => (obj[i]=cur,obj), {});
?
You could use an accumulator aka reduce
.
['a','b','c'].reduce(function(result, item, index, array) {
result[index] = item; //a, b, c
return result;
}, {}) //watch out the empty {}, which is passed as "result"
Pass an empty object {}
as a starting point; then "augment" that object incrementally. At the end of the iterations, result
will be {"0": "a", "1": "b", "2": "c"}
If your array is a set of key-value pair objects:
[{ a: 1},{ b: 2},{ c: 3}].reduce(function(result, item) {
var key = Object.keys(item)[0]; //first property: a, b, c
result[key] = item[key];
return result;
}, {});
will produce: {a: 1, b: 2, c: 3}
For the sake of completeness, reduceRight
allows you to iterate over your array in reverse order:
[{ a: 1},{ b: 2},{ c: 3}].reduceRight(/* same implementation as above */)
will produce: {c:3, b:2, a:1}
Your accumulator can be of any type for you specific purpose. For example in order to swap the key and value of your object in an array, pass []
:
[{ a: 1},{ b: 2},{ c: 3}].reduce(function(result, item, index) {
var key = Object.keys(item)[0]; //first property: a, b, c
var value = item[key];
var obj = {};
obj[value] = key;
result.push(obj);
return result;
}, []); //an empty array
will produce: [{1: "a"}, {2: "b"}, {3: "c"}]
Unlike map
, reduce
may not be used as a 1-1 mapping. You have full control over the items you want to include or exclude. Therefore reduce
allows you to achieve what filter
does, which makes reduce
very versatile:
[{ a: 1},{ b: 2},{ c: 3}].reduce(function(result, item, index) {
if(index !== 0) { //skip the first item
result.push(item);
}
return result;
}, []); //an empty array
will produce: [{2: "b"}, {3: "c"}]
Caution: reduce
and Object.key
are part of ECMA 5th edition
; you should provide a polyfill for browsers that don't support them (notably IE8).
See a default implementation by Mozilla.
If you're using jquery:
$.extend({}, ['a', 'b', 'c']);
{0: 'a', 1: 'b', 2: 'c'}
what is an expected result.
For completeness, ECMAScript 2015(ES6) spreading. Will require either a transpiler(Babel) or an environment running at least ES6.
console.log( { ...['a', 'b', 'c'] } )
I'd probably write it this way (since very rarely I'll not be having the underscorejs library at hand):
var _ = require('underscore');
var a = [ 'a', 'b', 'c' ];
var obj = _.extend({}, a);
console.log(obj);
// prints { '0': 'a', '1': 'b', '2': 'c' }
obj=_.extend({},a);
would do the job. Also, if you are iterating through arrays I’d say _.each
would be more appropriate than _.map
. All in all, this is not a good answer on several levels.
In case you want to use one of the properties of the iterated objects as key, for example:
// from:
const arr = [
{
sid: 123,
name: 'aaa'
},
{
sid: 456,
name: 'bbb'
},
{
sid: 789,
name: 'ccc'
}
];
// to:
{
'123': { sid: 123, name: 'aaa' },
'456': { sid: 456, name: 'bbb' },
'789': { sid: 789, name: 'ccc' }
}
Use:
const result = arr.reduce((obj, cur) => ({...obj, [cur.sid]: cur}), {})
we can use Object.assign
and array.reduce
function to convert an Array to Object.
var arr = [{a:{b:1}},{c:{d:2}}] var newObj = arr.reduce((a, b) => Object.assign(a, b), {}) console.log(newObj)
arr = [{ b: 1, d: 2 }]
to obj.
Here is an O(1) ES2015 method just for completeness.
var arr = [1, 2, 3, 4, 5]; // array, already an object
Object.setPrototypeOf(arr, Object.prototype); // now no longer an array, still an object
length
property. (3) The object is still an array, Array.isArray(arr) === true
. (4) Special array behaviors are not removed, e.g. arr.length = 0
removes all indices. (5) Therefore, I think Object.assign
is much better.
Array.isArray
is returning true
for the "object" here even though instanceof Array
does not...
FWIW, one another recent approach is to use the new Object.fromEntries
along with Object.entries
as follows:
const arr = ['a','b','c'];
arr[-2] = 'd';
arr.hello = 'e';
arr.length = 17;
const obj = Object.fromEntries(Object.entries(arr));
...which allows for avoiding storing sparse array items as undefined
or null
and preserves non-index (e.g., non-positive-integer/non-numeric) keys.
{ 0: "a", 1: "b", 2: "c", "-2": "d", hello: "e" }
(Same result here as with @Paul Draper's Object.assign
answer.)
One may wish to add arr.length
, however, as that is not included:
obj.length = arr.length;
arr.entries()
instead of Object.entries(arr)
Using javascript#forEach
one can do this
var result = {},
attributes = ['a', 'b','c'];
attributes.forEach(function(prop,index) {
result[index] = prop;
});
With ECMA6:
attributes.forEach((prop,index)=>result[index] = prop);
If you're using ES6, you can use Object.assign and the spread operator
{ ...['a', 'b', 'c'] }
If you have nested array like
var arr=[[1,2,3,4]]
Object.assign(...arr.map(d => ({[d[0]]: d[1]})))
new Map([['key1', 'value1'], ['key2', 'value2']]);
A quick and dirty one:
var obj = {},
arr = ['a','b','c'],
l = arr.length;
while( l && (obj[--l] = arr.pop() ) ){};
{0:"c", 1:"b", 2:"a"}
. You either want unshift
instead of pop
or (better) start with i=arr.length-1
and decrement instead.
l = arr.length
, and then while (l && (obj[--l] = arr.pop())){}
(I realize this is old, but why not simplify it even further).
Quick and dirty #2:
var i = 0
, s = {}
, a = ['A', 'B', 'C'];
while( i < a.length ) { s[i] = a[i++] };
i < a.length
instead of a[i]
.
More browser supported and more flexible way of doing that is using a normal loop, something like:
const arr = ['a', 'b', 'c'],
obj = {};
for (let i=0; i<arr.length; i++) {
obj[i] = arr[i];
}
But also the modern way could be using the spread operator, like:
{...arr}
Or Object assign:
Object.assign({}, ['a', 'b', 'c']);
Both will return:
{0: "a", 1: "b", 2: "c"}
A simple and cheeky method of quickly converting an Array of items in to an Object
function arrayToObject( srcArray ){
return JSON.parse( JSON.stringify( srcArray ) );
}
Then using it like so...
var p = [0,2,3,'pork','pie',6];
obj = new arrayToObject( p );
console.log( obj[3], obj[4] )
// expecting `pork pie`
Output:
pork pie
Checking the type:
typeof obj
"object"
AND things wouldn't be complete if there wasn't a prototype method
Array.prototype.toObject =function(){
return JSON.parse( JSON.stringify( this ) );
}
Using like:
var q = [0,2,3,'cheese','whizz',6];
obj = q.toObject();
console.log( obj[3], obj[4] )
// expecting `cheese whizz`
Output:
cheese whizz
*NOTE that there is no naming routine, so if you want to have specific names, then you will need to continue using the existing methods below.
Older method
This allows you to generate from an array an object with keys you define in the order you want them.
Array.prototype.toObject = function(keys){
var obj = {};
var tmp = this; // we want the original array intact.
if(keys.length == this.length){
var c = this.length-1;
while( c>=0 ){
obj[ keys[ c ] ] = tmp[c];
c--;
}
}
return obj;
};
result = ["cheese","paint",14,8].toObject([0,"onion",4,99]);
console.log(">>> :" + result.onion);
will output "paint", the function has to have arrays of equal length or you get an empty object.
Here is an updated method
Array.prototype.toObject = function(keys){
var obj = {};
if( keys.length == this.length)
while( keys.length )
obj[ keys.pop() ] = this[ keys.length ];
return obj;
};
.reduce((o,v,i)=>(o[i]=v,o), {})
[docs]
or more verbose
var trAr2Obj = function (arr) {return arr.reduce((o,v,i)=>(o[i]=v,o), {});}
or
var transposeAr2Obj = arr=>arr.reduce((o,v,i)=>(o[i]=v,o), {})
shortest one with vanilla JS
JSON.stringify([["a", "X"], ["b", "Y"]].reduce((o,v,i)=>{return o[i]=v,o}, {}))
=> "{"0":["a","X"],"1":["b","Y"]}"
some more complex example
[["a", "X"], ["b", "Y"]].reduce((o,v,i)=>{return o[v[0]]=v.slice(1)[0],o}, {})
=> Object {a: "X", b: "Y"}
even shorter (by using function(e) {console.log(e); return e;}
=== (e)=>(console.log(e),e)
)
nodejs
> [[1, 2, 3], [3,4,5]].reduce((o,v,i)=>(o[v[0]]=v.slice(1),o), {})
{ '1': [ 2, 3 ], '3': [ 4, 5 ] }
[/docs]
[/docs]
? It would be more useful to make the code snippets executable.
As of Lodash 3.0.0 you can use _.toPlainObject
var obj = _.toPlainObject(['a', 'b', 'c']); console.log(obj);
If you can use Map
or Object.assign
, it's very easy.
Create an array:
const languages = ['css', 'javascript', 'php', 'html'];
The below creates an object with index as keys:
Object.assign({}, languages)
Replicate the same as above with Maps
Converts to an index based object {0 : 'css'}
etc...
const indexMap = new Map(languages.map((name, i) => [i, name] ));
indexMap.get(1) // javascript
Convert to an value based object {css : 'css is great'}
etc...
const valueMap = new Map(languages.map(name => [name, `${name} is great!`] ));
valueMap.get('css') // css is great
If someone is searching for a Typescript method, i wrote this:
const arrayToObject = <T extends Record<K, any>, K extends keyof any>(
array: T[] = [],
getKey: (item: T) => K,
) =>
array.reduce((obj, cur) => {
const key = getKey(cur)
return ({...obj, [key]: cur})
}, {} as Record<K, T>)
It will:
enforce first param to be array of objects help to select the key enforce the key to be an key of all array items
Example:
// from:
const array = [
{ sid: 123, name: 'aaa', extra: 1 },
{ sid: 456, name: 'bbb' },
{ sid: 789, name: 'ccc' }
];
// to:
{
'123': { sid: 123, name: 'aaa' },
'456': { sid: 456, name: 'bbb' },
'789': { sid: 789, name: 'ccc' }
}
usage:
const obj = arrayToObject(array, item => item.sid) // ok
const obj = arrayToObject(array, item => item.extra) // error
${val}
; }, '') }) }, {} as Record<K, T>);
Here's a recursive function I just wrote. It's simple and works well.
// Convert array to object
var convArrToObj = function(array){
var thisEleObj = new Object();
if(typeof array == "object"){
for(var i in array){
var thisEle = convArrToObj(array[i]);
thisEleObj[i] = thisEle;
}
}else {
thisEleObj = array;
}
return thisEleObj;
}
Here's an example (jsFiddle):
var array = new Array();
array.a = 123;
array.b = 234;
array.c = 345;
var array2 = new Array();
array2.a = 321;
array2.b = 432;
array2.c = 543;
var array3 = new Array();
array3.a = 132;
array3.b = 243;
array3.c = 354;
var array4 = new Array();
array4.a = 312;
array4.b = 423;
array4.c = 534;
var array5 = new Array();
array5.a = 112;
array5.b = 223;
array5.c = 334;
array.d = array2;
array4.d = array5;
array3.d = array4;
array.e = array3;
console.log(array);
// Convert array to object
var convArrToObj = function(array){
var thisEleObj = new Object();
if(typeof array == "object"){
for(var i in array){
var thisEle = convArrToObj(array[i]);
thisEleObj[i] = thisEle;
}
}else {
thisEleObj = array;
}
return thisEleObj;
}
console.log(convArrToObj(array));
https://i.stack.imgur.com/KZHoT.png
['a' = '1', 'b' = '2', 'c' = '3']
and want it like {a: 1, b: 2, c: 3}
this works perfect.
I would do this simply with Array.of()
. Array of has the ability to use it's context as a constructor.
NOTE 2 The of function is an intentionally generic factory method; it does not require that its this value be the Array constructor. Therefore it can be transferred to or inherited by other constructors that may be called with a single numeric argument.
So we may bind Array.of()
to a function and generate an array like object.
function dummy(){}; var thingy = Array.of.apply(dummy,[1,2,3,4]); console.log(thingy);
By utilizing Array.of()
one can even do array sub-classing.
let i = 0; let myArray = ["first", "second", "third", "fourth"]; const arrayToObject = (arr) => Object.assign({}, ...arr.map(item => ({[i++]: item}))); console.log(arrayToObject(myArray));
Or use
myArray = ["first", "second", "third", "fourth"] console.log({...myArray})
ES5 - Solution:
Using Array prototype function 'push' and 'apply' you can populate the object with the array elements.
var arr = ['a','b','c']; var obj = new Object(); Array.prototype.push.apply(obj, arr); console.log(obj); // { '0': 'a', '1': 'b', '2': 'c', length: 3 } console.log(obj[2]); // c
{ name: a, div :b, salary:c}
Try using reflect to copy from array item to object.
var arr =['aa:23','bb:44','cc:55']
var obj ={}
arr.forEach(e => {
var ee = e.split(':')
Reflect.set(obj,ee[0],ee[1])
});
console.log(obj) // { aa: '23', bb: '44', cc: '55' }
You could use a function like this:
var toObject = function(array) {
var o = {};
for (var property in array) {
if (String(property >>> 0) == property && property >>> 0 != 0xffffffff) {
o[i] = array[i];
}
}
return o;
};
This one should handle sparse arrays more efficiently.
It's not directly relevant but I came here searching for a one liner for merging nested objects such as
const nodes = {
node1: {
interfaces: {if1: {}, if2: {}}
},
node2: {
interfaces: {if3: {}, if4: {}}
},
node3: {
interfaces: {if5: {}, if6: {}}
},
}
The solution is to use a combination of reduce and object spread:
const allInterfaces = nodes => Object.keys(nodes).reduce((res, key) => ({...res, ...nodes[key].interfaces}), {})
Object.fromEntries(Object.entries(nodes).map(([key, value] => [key, value.interfaces]))
Simplest way to do this is the following:
const arr = ['a','b','c'];
let obj = {}
function ConvertArr(arr) {
if (typeof(arr) === 'array') {
Object.assign(obj, arr);
}
This way it only runs if it is an array, however, you can run this with let global object variable or without, that's up to you, if you run without let, just do Object.assign({}, arr).
Use the javascript lodash library. There is a simple method _.mapKeys(object, [iteratee=_.identity])
that can do the conversion.
Here's a solution in coffeescript
arrayToObj = (arr) ->
obj = {}
for v,i in arr
obj[i] = v if v?
obj
obj[i] = v for v,i in arr when v?
Success story sharing
{ ...[sortedArray]}
reduce
like:arr.reduce((a, v) => ({ ...a, [v]: v}), {})