How to find index of an object by key and value in an javascript array
JavascriptJqueryJavascript Problem Overview
Given:
var peoples = [
{ "attr1": "bob", "attr2": "pizza" },
{ "attr1": "john", "attr2": "sushi" },
{ "attr1": "larry", "attr2": "hummus" }
];
Wanted:
Index of object where attr === value
for example attr1 === "john"
or attr2 === "hummus"
Update: Please, read my question carefully, i do not want to find the object via $.inArray nor i want to get the value of a specific object attribute. Please consider this for your answers. Thanks!
Javascript Solutions
Solution 1 - Javascript
The Functional Approach
All the cool kids are doing functional programming (hello React users) these days so I thought I would give the functional solution. In my view it's actually a lot nicer than the imperatival for
and each
loops that have been proposed thus far and with ES6 syntax it is quite elegant.
Update
There's now a great way of doing this called findIndex
which takes a function that return true
/false
based on whether the array element matches (as always, check for browser compatibility though).
var index = peoples.findIndex(function(person) {
return person.attr1 == "john"
});
With ES6 syntax you get to write this:
var index = peoples.findIndex(p => p.attr1 == "john");
The (Old) Functional Approach
TL;DR
If you're looking for index
where peoples[index].attr1 == "john"
use:
var index = peoples.map(function(o) { return o.attr1; }).indexOf("john");
Explanation
Step 1
Use .map()
to get an array of values given a particular key:
var values = object_array.map(function(o) { return o.your_key; });
The line above takes you from here:
var peoples = [
{ "attr1": "bob", "attr2": "pizza" },
{ "attr1": "john", "attr2": "sushi" },
{ "attr1": "larry", "attr2": "hummus" }
];
To here:
var values = [ "bob", "john", "larry" ];
Step 2
Now we just use .indexOf()
to find the index of the key we want (which is, of course, also the index of the object we're looking for):
var index = values.indexOf(your_value);
Solution
We combine all of the above:
var index = peoples.map(function(o) { return o.attr1; }).indexOf("john");
Or, if you prefer ES6 syntax:
var index = peoples.map((o) => o.attr1).indexOf("john");
Demo:
var peoples = [
{ "attr1": "bob", "attr2": "pizza" },
{ "attr1": "john", "attr2": "sushi" },
{ "attr1": "larry", "attr2": "hummus" }
];
var index = peoples.map(function(o) { return o.attr1; }).indexOf("john");
console.log("index of 'john': " + index);
var index = peoples.map((o) => o.attr1).indexOf("larry");
console.log("index of 'larry': " + index);
var index = peoples.map(function(o) { return o.attr1; }).indexOf("fred");
console.log("index of 'fred': " + index);
var index = peoples.map((o) => o.attr2).indexOf("pizza");
console.log("index of 'pizza' in 'attr2': " + index);
Solution 2 - Javascript
If you want to check on the object itself without interfering with the prototype, use hasOwnProperty()
:
var getIndexIfObjWithOwnAttr = function(array, attr, value) {
for(var i = 0; i < array.length; i++) {
if(array[i].hasOwnProperty(attr) && array[i][attr] === value) {
return i;
}
}
return -1;
}
to also include prototype attributes, use:
var getIndexIfObjWithAttr = function(array, attr, value) {
for(var i = 0; i < array.length; i++) {
if(array[i][attr] === value) {
return i;
}
}
return -1;
}
Solution 3 - Javascript
Using jQuery .each()
var peoples = [
{ "attr1": "bob", "attr2": "pizza" },
{ "attr1": "john", "attr2": "sushi" },
{ "attr1": "larry", "attr2": "hummus" }
];
$.each(peoples, function(index, obj) {
$.each(obj, function(attr, value) {
console.log( attr + ' == ' + value );
});
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
Using for-loop:
var peoples = [ { "attr1": "bob", "attr2": "pizza" }, { "attr1": "john", "attr2": "sushi" }, { "attr1": "larry", "attr2": "hummus" }];
for (var i = 0; i < peoples.length; i++) {
for (var key in peoples[i]) {
console.log(key + ' == ' + peoples[i][key]);
}
}
Solution 4 - Javascript
Not a direct answer to your question, though I thing it's worth mentioning it, because your question seems like fitting in the general case of "getting things by name in a key-value storage".
If you are not tight to the way "peoples" is implemented, a more JavaScript-ish way of getting the right guy might be :
var peoples = {
"bob": { "dinner": "pizza" },
"john": { "dinner": "sushi" },
"larry" { "dinner": "hummus" }
};
// If people is implemented this way, then
// you can get values from their name, like :
var theGuy = peoples["john"];
// You can event get directly to the values
var thatGuysPrefferedDinner = peoples["john"].dinner;
Hope if this is not the answer you wanted, it might help people interested in that "key/value" question.
Solution 5 - Javascript
function getIndexByAttribute(list, attr, val){
var result = null;
$.each(list, function(index, item){
if(item[attr].toString() == val.toString()){
result = index;
return false; // breaks the $.each() loop
}
});
return result;
}
Solution 6 - Javascript
You can also make it a reusable method by expending JavaScript:
Array.prototype.findIndexBy = function(key, value) {
return this.findIndex(item => item[key] === value)
}
const peoples = [{name: 'john'}]
const cats = [{id: 1, name: 'kitty'}]
peoples.findIndexBy('name', 'john')
cats.findIndexBy('id', 1)
Solution 7 - Javascript
Do this way:-
var peoples = [
{ "name": "bob", "dinner": "pizza" },
{ "name": "john", "dinner": "sushi" },
{ "name": "larry", "dinner": "hummus" }
];
$.each(peoples, function(i, val) {
$.each(val, function(key, name) {
if (name === "john")
alert(key + " : " + name);
});
});
OUTPUT:
name : john
Refer LIVE DEMO
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