reducing array elements using underscore.js

Question

I am getting an array of data containing many parameters. For example, the data array is in the below format:

var data  = [
             {
               "name":"pradeep", 
               "age": "32", 
               "location": "Bangalore"
             }, 
             {
               "name":"praveen", 
               "age": "30", 
               "location": "Mangalore"
             }, 
             {
               "name":"Ajay", 
               "age": "32", 
               "location": "Hubli"
             }
           ]

I want the above array to be reduced to the below format:

     [
             {
               "name":"pradeep"
             }, 
             {
               "name":"praveen"
             }, 
             {
               "name":"Ajay"
             }
           ]

How to get this done using Underscore. I tried using the _.pluck but it fetches only the data and not the key.

Check out the _.pick or _.omit functions. They are functions that filter objects. — Denis Frezzato
– Denis Frezzato, Commented Jan 11, 2016 at 17:15
@DenisFrezzato I wrote an answer recommending _.pick, then I realised the OP wants an array of objects and pick only works on single objects. — Alnitak
– Alnitak, Commented Jan 11, 2016 at 17:17
It can be achieved using _.map to loop through the array and _.pick to filter the object. — Denis Frezzato
– Denis Frezzato, Commented Jan 11, 2016 at 17:20
@DenisFrezzato indeed, but it's hardly efficient. _.pick() is best suited for when there are multiple keys to be copied, and/or when the keyname is variable. — Alnitak
– Alnitak, Commented Jan 11, 2016 at 17:22

yonki · Accepted Answer · 2016-01-11 17:17:30Z

1

You could use pure JavaScript to do it, one way is:

data.map(function(obj) { 
    return {'name': obj.name};
})

If you'd like to parametrize key that should be kept, you may write function like that:

function filterByKey(arr, key) {
    return arr.map(function(obj) {
        var newObj = {};
        newObj[key] = obj[key];
        return newObj;
    });
}

and use it like that:

var newData = filterByKey(data, 'name');

Cheers

answered Jan 11, 2016 at 17:17

yonki

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Comments

iplus26 · Accepted Answer · 2016-01-11 17:14:22Z

0

In native JavaScript, you can do it like:

var data = [{
  "name": "pradeep",
  "age": "32",
  "location": "Bangalore"
}, {
  "name": "praveen",
  "age": "30",
  "location": "Mangalore"
}, {
  "name": "Ajay",
  "age": "32",
  "location": "Hubli"
}];

var newData = data.map(function(d) {
  return { name: d.name }
});

console.log(newData)

answered Jan 11, 2016 at 17:14

iplus26

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Comments

Steven Schobert · Accepted Answer · 2016-01-11 17:16:44Z

0

Underscore is not really required, you can do this..

var newData = data.map(function (x) {
    return { name: x.name };
});

but if you really want to use underscore this is the way:

var newData = _.map(data, function (x) {
    return { name: x.name };
});

edited Jan 11, 2016 at 17:16

Steven Schobert

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answered Jan 11, 2016 at 17:14

martskins

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Comments

Alnitak · Accepted Answer · 2016-01-11 17:21:21Z

0

For a strictly underscore JS method you can use _.map combined with _.pick:

var newData = _.map(data, function(d) { return _.pick(d, 'name' })

However using _.pick will not be as efficient as just simply returning { name: d.name } in the _.map callback.

edited Jan 11, 2016 at 17:21

answered Jan 11, 2016 at 17:14

Alnitak

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Comments

nstoitsev · Accepted Answer · 2016-01-11 17:22:50Z

0

You need to use the map function from Undescore. It's a very popular utility from the functional programming and you can also use it natively in the browser.

With Underscore.js the code looks like this:

_.map(data, function(element) {
  return {name: element['name']};
})

answered Jan 11, 2016 at 17:22

nstoitsev

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Comments

srinivas · Accepted Answer · 2016-01-11 17:31:09Z

0

You can do it using native JavaScript

var result = [];
data.forEach(function(d){
 result.push({'name': d.name}) // d is an iterator
})

You could as use map function to return the key value pair

var result = data.map(function(d){
 return {'name': d.name}
})

edited Jan 11, 2016 at 17:31

answered Jan 11, 2016 at 17:25

srinivas

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