Delete an element from an Array based on a condition block and return that element

Question

Is there a quick Ruby or Rails method to delete an element from an Array based on a condition provided in a block and then return that element?

Let's say, given:

e1.good? # false
e2.good? # true
e3.good? # true
a = [e1, e2, e3]

Is there a method delete_and_return_if doing this:

a.delete_and_return_if { |e| e.good? }      # delete e2 from a and returns e2
[e1].delete_and_return_if { |e| e.good? }   # returns nil

Or at least is there a clean way to do this?

Benoît · Accepted Answer · 2012-12-06 06:20:27Z

1

If you do not have duplicates or that you want to delete all same elements, you can do

a.delete(a.detect(&:good?))

a.detect(&:good?) will return the first good? object or nil if there is none.
a.delete(elem) will delete and return your element.

Or if you have duplicates and only want to delete the first one:

a.delete(a.index(a.detect(&:good?)))

edited Dec 6, 2012 at 6:20

answered Dec 6, 2012 at 6:15

Benoît

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2 Comments

Innerpeacer Over a year ago

So I guess this is the cleanest solution we have in Ruby? One thing that is not so perfect is that it has to take two iterations :)

Benoît Over a year ago

@Innerpeacer You could do return a.clone - a.delete_if(&:good?) if you want.

Jonathan Vukovich-Tribouharet · Accepted Answer · 2012-12-06 05:59:09Z

1

There is delete_if, this is a Ruby function. http://www.ruby-doc.org/core-1.9.3/Array.html

answered Dec 6, 2012 at 5:59

Jonathan Vukovich-Tribouharet

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1 Comment

Innerpeacer Over a year ago

Unfortunately, delete_if return the array itself, not the element being deleted.

vijikumar · Accepted Answer · 2012-12-06 06:02:32Z

1

 a = [e1, e2, e3]

 a.delete_if{|e|!e.good?}

 it will delete e1. and returns e2 and e3

answered Dec 6, 2012 at 6:02

vijikumar

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Comments

score 1 · Accepted Answer · 2012-12-06 06:21:24Z

1

This will update array and return deleted entry:

a = [1, 2, 3]

p a
# => [1, 2, 3]

deleted = a.delete a.detect {|e| e == 2 }
p deleted
# => 2

p a
# => [1, 3]

so you can do like this:

a.delete a.detect(&:good?)

UPDATE: thanks to @oldergod for recalling me about detect

edited Dec 6, 2012 at 6:21

answered Dec 6, 2012 at 6:05

user904990

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