Get the min and max from array of objects with underscore.js

Question

Let's say I have the following structure

var myArrofObjects =  [
    {prop1:"10", prop2:"20", prop3: "somevalue1"},
    {prop1:"11", prop2:"26", prop3: "somevalue2"},
    {prop1:"67", prop2:"78", prop3: "somevalue3"} ];

I need to find the min and max based on prop2, so here my numbers would be 20 and 78.

How can I write code in Underscore to do that?

I'd probably just each and set min/max vals; there's no "min/max" just min and max. Sorting would take longer, but you could always sort and take first/last vals. — Dave Newton
– Dave Newton, Commented Oct 26, 2015 at 17:32
@Andreas. Yes, i know of these functions existence. However, I am asking something more specific, see question. — sarsnake
– sarsnake, Commented Oct 26, 2015 at 17:34
@Dave, I am not sure what min/max is. I need a min and a max. As in, 2 different values. I think the question is pretty clear. — sarsnake
– sarsnake, Commented Oct 26, 2015 at 17:35
@sarsnake: It's a hypothetical function that returns the min and max at the same time. But anyway, why isn't _min and _max good enough? — Jon
– Jon, Commented Oct 26, 2015 at 17:36

score 13 · Accepted Answer · 2015-10-26 18:09:31Z

13

You don't really need underscore for something like this.

Math.max(...arrayOfObjects.map(elt => elt.prop2));

If you're not an ES6 kind of guy, then

Math.max.apply(0, arrayOfObjects.map(function(elt) { return elt.prop2; }));

Use the same approach for minimum.

If you're intent on finding max and min at the same time, then

arrayOfObjects . 
  map(function(elt) { return elt.prop2; }) .
  reduce(function(result, elt) {
    if (elt > result.max) result.max = elt;
    if (elt < result.min) result.min = elt;
    return result;
  }, { max: -Infinity, min: +Infinity });

edited Oct 26, 2015 at 18:09

answered Oct 26, 2015 at 18:03

user663031

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3 Comments

Richard Over a year ago

You do need Underscore if you want compatibility in older browsers.

user663031 Over a year ago

Umm, which older browser?

ajliptak Over a year ago

As a note, max returns -Infinity for empty arrays.

Nadeeshaan · Accepted Answer · 2017-11-07 06:10:28Z

7

You can use the _.maxBy to find max value as follows.

var maxValObject = _.maxBy(myArrofObjects, function(o) { return o.prop2; });

or with the iteratee shorthand as follows

var maxValObject = _.maxBy(myArrofObjects, 'prop2');

similarly the _.minBy as well;

Ref: https://lodash.com/docs/4.17.4#maxBy

answered Nov 7, 2017 at 6:10

Nadeeshaan

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Comments

Meir · Accepted Answer · 2015-10-26 17:58:22Z

2

use _.max and _.property:

var max value = _.max(myArrofObjects, _.property('prop2'));

answered Oct 26, 2015 at 17:58

Meir

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Comments

ykay says Reinstate Monica · Accepted Answer · 2016-03-20 15:37:22Z

2

Use _.max as follows:

var max_object = _.max(myArrofObjects, function(object){return object.prop2})

Using a function as the second input will allow you to access nested values in the object as well.

answered Mar 20, 2016 at 15:37

ykay says Reinstate Monica

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1 Comment

Dunc Over a year ago

Probably obvious, but note you need to do max_object.prop2 to get the max value (since this returns the whole object).

svarog · Accepted Answer · 2015-10-26 18:03:57Z

0

Underscore

use _.sortBy(..) to sort your object by a property

var sorted = _.sortBy(myArrofObjects, function(item){
    return item.prop2;
});

you will then get a sorted array by your prop1 property, sorted[0] is the min, and sorted[n] is the max

Plain JS

myArrofObjects.sort(function(a, b) {
    return a.prop2 - b.prop2;
})

edited Oct 26, 2015 at 18:03

answered Oct 26, 2015 at 17:59

svarog

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3 Comments

user663031 Over a year ago

In the first example, I guess it should be prop2.

user663031 Over a year ago

I can't really agree with this solution. You are doing a potentially expensive sort only to find the min and max.

svarog Over a year ago

yes, the idea is to have a sorted array for other future operations. I don't know OP's use case, but that's what I would have done

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