10
# this code works
list = (0..20).to_a
# => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20] 

odd = list.select { |x| x.odd? }
# => [1, 3, 5, 7, 9, 11, 13, 15, 17, 19] 

list.reject! { |x| x.odd? }
# => [0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20] 

# but can i emulate this type of functionality with an enumerable method?
set = [1,5,10]
# => [1, 5, 10] 
one, five, ten = set
# => [1, 5, 10] 
one
# => 1 
five
# => 5 
ten
# => 10

# ------------------------------------------------
# method I am looking for ?
list = (0..20).to_a
odd, even = list.select_with_reject { |x| x.odd? }
# put the matching items into the first variable
# and the non-matching into the second
house9
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  • Built in methods are nice, but are you opposed to adding your own method to `Array` that would do this? – MrDanA Apr 05 '13 at 23:47
  • yes, i was thinking about monkey patching Array to add it - seems like something ruby might already have built in, but didn't see anything in the docs – house9 Apr 05 '13 at 23:50

4 Answers4

20

Sure, you can do:

odd, even = list.partition &:odd?
pguardiario
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  • awesome - thanks; interesting it shows up on the enumerable docs - http://ruby-doc.org/core-1.9.2/Enumerable.html but not on array? – house9 Apr 05 '13 at 23:59
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    @house9 Enumerable is a mixin, so many classes can use it. Hashes use them too. – MrDanA Apr 06 '13 at 04:57
  • That's because it is defined on `Enumerable` but not on `Array`. This is called *inheritance* and is one of the fundamental concepts of Ruby and many other languages, not just object-oriented ones. – Jörg W Mittag Apr 06 '13 at 07:51
1
odd = []
even = []
list = [1..20]
list.each {|x| x.odd? ? odd << x : even << x }
duggiefresh
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1

As pguardiario said, the partition method is the most direct way. You could also use Set#divide:

require 'set'
list = (1..10).to_a
odd, even = Set.new(list).divide(&:odd?).to_a.map{|x| x.to_a}
alf
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1

You could try below:

odd,even = (0..20).group_by(&:odd?).values
p odd,even

Output:

[0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20]
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19]
Arup Rakshit
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