How do I test if one array is a subset of another? [closed]

Question

What's the best (cleanest) way to provide this sort of logic?

var colors = ["red","white","blue"];

logic(colors,["red","green"]); //false
logic(colors,["red"]); //true
logic(colors,["red","purple"]); //false
logic(colors,["red","white"]); //true
logic(colors,["red","white","blue"]); //true
logic(colors,["red","white","blue","green"]); //false
logic(colors,["orange"]); //false

Possibly using underscore.js?

Looks like he is trying to determine if the array given has only the elements of the colors array in it. — MrZander
– MrZander, Commented Jan 2, 2013 at 22:23

Felix Kling · Accepted Answer · 2013-01-02 22:26:28Z

46

Assuming each element in the array is unique: Compare the length of hand with the length of the intersection of both arrays. If they are the same, all elements in hand are also in colors.

var result = (hand.length === _.intersection(hand, colors).length);

DEMO

edited Jan 2, 2013 at 22:26

answered Jan 2, 2013 at 22:21

Felix Kling

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3 Comments

ThomasReggi Over a year ago

Thanks, no matter how many times I read the underscore docs I can rarely think of these solutions when I need them.

timaschew Over a year ago

as you say it's not working if the lements are not unique and it also doesn't work if you want to check the order: I created I gist to solve it with these needs: gist.github.com/timaschew/891632094c8bfcb73c38

Mahesh K Over a year ago

_.difference(subset, superset).length === 0

Sergey Berezovskiy · Accepted Answer · 2013-01-02 22:29:58Z

22

Maybe difference is what you are looking for:

_(hand).difference(colors).length === 0

edited Jan 2, 2013 at 22:29

answered Jan 2, 2013 at 22:20

Sergey Berezovskiy

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2 Comments

Felix Kling Over a year ago

It should be _(hand).difference(colors).length === 0;: jsfiddle.net/GXGun/1 (you got it vice versa ;)). Nice solution though!

Raj Nathani Over a year ago

return !_(hand).difference(colors).length

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