Lodash: Convert array with duplicate values to object with number of repeated occurrences

Question

Here is my array:

['California','Texas','Texas','Texas','New York','Missouri','New Mexico','California']

Is there a way in lodash to convert it to an object with a count of repeated occurrences like this:

[
    {'name':'California', 'count':2},
    {'name':'Texas', 'count':3},
    {'name':'New York', 'count':1},
    {'name':'Missouri', 'count':1},
    {'name':'New Mexico', 'count':1},
]

I have tried many combinations but have not been successful. Docs: https://lodash.com/docs#countBy

What have you tried? Seems to me that countBy works, you just have to slightly modify the result after it's done — VLAZ
– VLAZ, Commented Aug 30, 2016 at 16:11
Since you only have two properties maybe it would work better as {California: 2, Texas: 3} -- just a suggestion — Explosion Pills
– Explosion Pills, Commented Aug 30, 2016 at 16:18
@ExplosionPills this is exactly what countBy produces if you call it with no other arguments than the data in this post — VLAZ
– VLAZ, Commented Aug 30, 2016 at 16:20

Nina Scholz · Accepted Answer · 2016-08-30 16:37:21Z

4

You could just map the result of _.countBy.

var array = ['California','Texas','Texas','Texas','New York','Missouri','New Mexico','California'],
    count = _.countBy(array),
    result = _.map(count, (v, k) => ({ name: k, count: v }));

console.log(count);
console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.15.0/lodash.min.js"></script>

Combined with _.chain

var array = ['California','Texas','Texas','Texas','New York','Missouri','New Mexico','California'],
    count = _
        .chain(array)
        .countBy()
        .map((v, k) => ({ name: k, count: v }));

console.log(count);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.15.0/lodash.min.js"></script>

edited Aug 30, 2016 at 16:37

answered Aug 30, 2016 at 16:22

Nina Scholz

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2 Comments

VLAZ Over a year ago

If you _.chain the calls, it'd be ever so slightly more performant, since you don't need the interim values. It makes the code look a bit tidier, too (again - no interim values). _.reduce might be a bit more idiomatic for this sort of thing.

comixninja Over a year ago

Thanks for a solution with Lodash! Just a heads up, the variables 'k' and 'v' above need to switch. Otherwise it says: { name:3, count:'Texas' }

Nenad Vracar · Accepted Answer · 2016-08-30 16:16:41Z

1

You can do this with reduce()

var ar = ['California','Texas','Texas','Texas','New York','Missouri','New Mexico','California'];

var obj = {}
var result = ar.reduce(function(r, e) {
  if(!obj[e]) {
    obj[e] = {name: e, count: 0};
    r.push(obj[e])
  }
  obj[e].count++;
  return r;
}, [])

console.log(result)

answered Aug 30, 2016 at 16:16

Nenad Vracar

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Comments

score 0 · Accepted Answer · 2016-08-30 16:21:04Z

0

I am not sure there is a built-in function to achieve it, but you can do it using standard method.

var arr = ['California', 'Texas', 'Texas', 'Texas', 'New York', 'Missouri', 'New Mexico', 'California'];
var obj = [];

arr.forEach(a => {
    var b = obj.find(b => b.name == a);
    if(!b){
        obj.push({
            name: a,
            count: 1
        });
    }else{
        b.count++;
    }
});

console.log(JSON.stringify(obj, null, 2));

edited Aug 30, 2016 at 16:21

answered Aug 30, 2016 at 16:13

user6586783

2 Comments

VLAZ Over a year ago

You can use find instead of filter. It more precisely what you want.

user6586783 Over a year ago

@Vld Updated answer.

Simone Poggi · Accepted Answer · 2016-08-30 16:29:06Z

0

As you said there's the countBy function for that, you have to map the result to set the format as required:

var result = _( array )
  .countBy( )
  .map( ( key, value ) => ( { name: key, count: value } ) )
  .value( )

console.log( result );

edited Aug 30, 2016 at 16:29

answered Aug 30, 2016 at 16:18

Simone Poggi

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2 Comments

VLAZ Over a year ago

OP already mentioned it. Also, you don't need the second parameter - it defaults to the same.

Simone Poggi Over a year ago

right, I didn't noticed, I'll update the answer then

Redu · Accepted Answer · 2016-08-30 16:35:31Z

0

Pure JS in just two lines.

var arr = ['California','Texas','Texas','Texas','New York','Missouri','New Mexico','California'],
    lut = arr.reduce((p,c) => p[c] ? (p[c]++ ,p) : (p[c] = 1, p),{});
 result = Object.keys(lut).map(k => ({name:k,count:lut[k]}));
console.log(result);

answered Aug 30, 2016 at 16:35

Redu

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Comments

Nina Scholz · Accepted Answer · 2016-08-30 17:22:02Z

0

In plain Javascript, you could use Array#forEach for it.

var data = ['toString', 'California', 'Texas', 'Texas', 'Texas', 'New York', 'Missouri', 'New Mexico', 'California'],
    count = [];

data.forEach(function (a) {
    if (!this[a]) {
        this[a] = { name: a, count: 0 };
        count.push(this[a]);
    }
    this[a].count++;
}, Object.create(null));

console.log(count)

.as-console-wrapper { max-height: 100% !important; top: 0; }

Version with {}

var data = ['toString', 'California', 'Texas', 'Texas', 'Texas', 'New York', 'Missouri', 'New Mexico', 'California'],
    count = [];

data.forEach(function (a) {
    if (!this[a]) {
        this[a] = { name: a, count: 0 };
        count.push(this[a]);
    }
    this[a].count++;
}, {}); // no Object.create(null)!

console.log(count)

.as-console-wrapper { max-height: 100% !important; top: 0; }

edited Aug 30, 2016 at 17:22

answered Aug 30, 2016 at 16:18

Nina Scholz

388k26 gold badges367 silver badges417 bronze badges

5 Comments

user6586783 Over a year ago

It would be better if you join your answers or delete this one.

Nenad Vracar Over a year ago

Is there a reason why you use Object.create(null) and not just {}

Nina Scholz Over a year ago

@NenadVracar, you could count over toString and that would not go without a really empty object.

user6586783 Over a year ago

@NinaScholz The only property of an object created with {} is __proto__. Function toString is actually the property of {}.__proto__.constructor.prototype.

Nina Scholz Over a year ago

@SoftwareEngineer171, please watch the difference of example one and two. keep an eye on toString.

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