Get the object in an array of object with the key

Question

So I have an array of objects and I want to get the object with the key "Z".

Obviously I can just loop through the array and check each key one by one and grab the one which matches, but I was thinking that there is probably a better way than my current approach:

for (var i = 0; i < data.length; i++) {
    if (Object.keys(data[i]).toString() == "z") {
        return data[i].z;
        break;
    }
}

My data:

"data": [
  { "X": { "foo": "bar1" } },
  { "Y": { "foo": "bar2" } },
  { "Z": { "foo": "bar3" } }
]

Desired Output:

{
  "foo": "bar3"
}

There is no better way, if you don't know where the key is, you have to iterate and look for it — adeneo
– adeneo, Commented Feb 26, 2015 at 20:12
Reorganize your data into a single object instead of an array of objects. — Blazemonger
– Blazemonger, Commented Feb 26, 2015 at 20:14
A javascript object is a map. Map lookup is O(1). Array lookup is O(n). — Jim Cote
– Jim Cote, Commented Feb 26, 2015 at 20:18

user3310334 · Accepted Answer · 2015-02-26 20:22:56Z

2

Instead of an array of objects, you could replace it with an object:

"data": {
  "X": { "foo": "bar1" },
  "Y": { "foo": "bar2" },
  "Z": { "foo": "bar3" }
}

And then access your object like so:

data['Z']

as you can see, much neater.

I'm guessing you used an array originally for easy appending and so on, but it's just as easy with an object:

data['A'] = { "foo": "bar4" };

will create key "A" in data, and you can still loop through your object using for (... in ...) loops, i.e:

for (key in data) {
  console.log(data[key].foo);
}

should print

bar1
bar2
bar3
bar4

answered Feb 26, 2015 at 20:22

user3310334

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Comments

Adam Boduch · Accepted Answer · 2015-02-26 21:55:36Z

Using lodash, you could do something like:

var collection = [
    { X: { foo: 'bar1' } },
    { Y: { foo: 'bar2' } },
    { Z: { foo: 'bar3' } }
];

_(collection)
    .chain()
    .find(_.ary(_.partialRight(_.has, 'Z'), 1))
    .values()
    .first()
    .value()
// → { foo: 'bar3' }

An outline of what this chain is doing:

chain(): Enables explicit chaining. Otherwise, find() will return an unwrapped object, and we still have actions to perform.
find(): We pass in a callback that checks for the existence of the Z key. The callback itself is constructed using higher-order function utilities:
- ary(): Restricts the number of arguments passed to the function. We do this here because find() passes arguments that we don't care about to our callback.
- partialRight(): Provides the 'Z' argument to the has() function. This is the rightmost argument, meaning that each item in the collection is passed as the first argument.
- has(): Returns true if the Z key exists on an object.
values(): We don't care about the object key, only it's values.
first(): The values() function returns a collection, but we only want the first item in it. There should only ever be one item in the collection.

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