Underscore: Filtering on objects could return an object

Created on 1 Nov 2011 · 8Comments · Source: jashkenas/underscore

Hi,

Here is a common use-case for filter. Given

a = {35: true, 45: true, 55: false}

one would like to filter and get back only pairs which value is truish:

_.filter(a, function(val, key) {
  val === true;
});
// => {35: true, 45: true}

Currently, functions such as filter push(value) so one gets an array.

Is there any easy way to achieve this with a workaround, and if not, would you consider switching the return's type based on whether we're providing an object or a list?

change wontfix

Source

chikamichi

Most helpful comment

jk, just saw _.pick which is perfect for my use case

jtfairbank on 22 Sep 2015

👍2

All 8 comments

I just needed the same thing and this issue was the 2nd Google git I got when searching. The only problem with making _.filter on objects return objects is backwards compatibility...

wulczer on 7 Nov 2011

filter is a function that originates in ES5 ... and we certainly don't want to break basic compatibility with the spec.

To address the bigger picture: All Underscore.js enumerable function can take either objects or arrays, and all return arrays. Breaking consistency here would need to be done for all of the functions at once, not just one of them. The current API allows you to compose Underscore functions without having to worry about the input types.