find the array index of an object with a specific key value in underscore
Javascriptunderscore.jsJavascript Problem Overview
In underscore, I can successfully find an item with a specific key value
var tv = [{id:1},{id:2}]
var voteID = 2;
var data = _.find(tv, function(voteItem){ return voteItem.id == voteID; });
//data = { id: 2 }
but how do I find what array index that object occurred at?
Javascript Solutions
Solution 1 - Javascript
findIndex
was added in 1.8:
index = _.findIndex(tv, function(voteItem) { return voteItem.id == voteID })
See: http://underscorejs.org/#findIndex
Alternatively, this also works, if you don't mind making another temporary list:
index = _.indexOf(_.pluck(tv, 'id'), voteId);
Solution 2 - Javascript
Lo-Dash, which extends Underscore, has findIndex method, that can find the index of a given instance, or by a given predicate, or according to the properties of a given object.
In your case, I would do:
var index = _.findIndex(tv, { id: voteID });
Give it a try.
Solution 3 - Javascript
If you want to stay with underscore so your predicate function can be more flexible, here are 2 ideas.
Method 1
Since the predicate for _.find
receives both the value and index of an element, you can use side effect to retrieve the index, like this:
var idx;
_.find(tv, function(voteItem, voteIdx){
if(voteItem.id == voteID){ idx = voteIdx; return true;};
});
Method 2
Looking at underscore source, this is how _.find
is implemented:
_.find = _.detect = function(obj, predicate, context) {
var result;
any(obj, function(value, index, list) {
if (predicate.call(context, value, index, list)) {
result = value;
return true;
}
});
return result;
};
To make this a findIndex
function, simply replace the line result = value;
with result = index;
This is the same idea as the first method. I included it to point out that underscore uses side effect to implement _.find
as well.
Solution 4 - Javascript
I don't know if there is an existing underscore method that does this, but you can achieve the same result with plain javascript.
Array.prototype.getIndexBy = function (name, value) {
for (var i = 0; i < this.length; i++) {
if (this[i][name] == value) {
return i;
}
}
return -1;
}
Then you can just do:
var data = tv[tv.getIndexBy("id", 2)]
Solution 5 - Javascript
If your target environment supports ES2015 (or you have a transpile step, eg with Babel), you can use the native Array.prototype.findIndex().
Given your example
const array = [ {id:1}, {id:2} ]
const desiredId = 2;
const index = array.findIndex(obj => obj.id === desiredId);
Solution 6 - Javascript
you can use indexOf
method from lodash
var tv = [{id:1},{id:2}]
var voteID = 2;
var data = _.find(tv, function(voteItem){ return voteItem.id == voteID; });
var index=_.indexOf(tv,data);
Solution 7 - Javascript
Keepin' it simple:
// Find the index of the first element in array
// meeting specified condition.
//
var findIndex = function(arr, cond) {
var i, x;
for (i in arr) {
x = arr[i];
if (cond(x)) return parseInt(i);
}
};
var idIsTwo = function(x) { return x.id == 2 }
var tv = [ {id: 1}, {id: 2} ]
var i = findIndex(tv, idIsTwo) // 1
Or, for non-haters, the CoffeeScript variant:
findIndex = (arr, cond) ->
for i, x of arr
return parseInt(i) if cond(x)
Solution 8 - Javascript
This is to help lodash
users. check if your key is present by doing:
hideSelectedCompany(yourKey) {
return _.findIndex(yourArray, n => n === yourKey) === -1;
}
Solution 9 - Javascript
The simplest solution is to use lodash:
- Install lodash:
> npm install --save lodash
-
Use method findIndex:
const _ = require('lodash');
findIndexByElementKeyValue = (elementKeyValue) => {
return _.findIndex(array, arrayItem => arrayItem.keyelementKeyValue);
}
Solution 10 - Javascript
If you're expecting multiple matches and hence need an array to be returned, try:
_.where(Users, {age: 24})
If the property value is unique and you need the index of the match, try:
_.findWhere(Users, {_id: 10})
Solution 11 - Javascript
Array.prototype.getIndex = function (obj) {
for (var i = 0; i < this.length; i++) {
if (this[i][Id] == obj.Id) {
return i;
}
}
return -1;
}
List.getIndex(obj);
Solution 12 - Javascript
I got similar case but in contrary is to find the used key based on index of a given object's. I could find solution in underscore using Object.values
to returns object in to an array to get the occurred index.
var tv = {id1:1,id2:2};
var voteIndex = 1;
console.log(_.findKey(tv, function(item) {
return _.indexOf(Object.values(tv), item) == voteIndex;
}));
<script src="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.9.1/underscore-min.js"></script>
Solution 13 - Javascript
And If you want some particular key value from an object by id then use
var tv = [{id:1, name:"ABC"},{id:2, name:xyz}]
_.find(tv , {id:1}).value // retrun "ABC"