Removing elements from an array non-destructively

Question

Given an array arr and an object v, I want a copy of arr without the elements equal to v.

I found these two solutions:

newarr = arr.dup newarr.delete(v)

and

newarr = arr.reject {|a| a == v}

Is there an easier way to do it?

I wonder whether Ruby already has something like:

newarr = arr.without(v)

Note that Ruby 1.9 is no longer supported by the core Ruby team. If it's at all possible, migrate to something in the 2.x series. 2.4.1 is current. — tadman
– tadman, Commented Jul 18, 2017 at 15:52
Simply put, you are asking for a non-destructive version of delete. — sawa
– sawa, Commented Jul 18, 2017 at 16:11
@engineersmnky oops, I didn't read the documentation of Array#delete carefully and I ignored its return value. You are right. — axiac
– axiac, Commented Jul 18, 2017 at 17:24
grep_v may be useful but uses === instead of == so it's not the same thing. — Sagar Pandya
– Sagar Pandya, Commented Jul 19, 2017 at 0:51

Aleksei Matiushkin · Accepted Answer · 2017-07-18 15:46:57Z

9

[1, 2, 3, 4, 4, 5, 5] - [4] #⇒ [1, 2, 3, 5, 5]

If this is too cumbersome for you too, use:

[1, 2, 3, 4, 4, 5, 5].reject(&4.method(:==)) #⇒ [1, 2, 3, 5, 5]

answered Jul 18, 2017 at 15:46

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10 Comments

@MarkThomas Let me guess: Array#-? :)

Hint: I'm considering putting it on a list of things to reject in a code review :)

@MarkThomas yeah, the censorship, we know how it happens when the democracy to use shortcuts suffers under the yoke of the senior dictators!

@MarkThomas Liberty or Death .reject(&:==.to_proc.curry(2).call(4)) :)

That is why I have monkeypatched Object to alias method as m in all my projects. Once for all saving 5 chars!

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