From: "Christopher Özbek" <newsgroups@...>
Date: 2002-03-26T03:19:19+09:00
Subject: How to split an Array efficiently? + non-inplace Delete_if

Hi,
  I want to split an array depending on the evaluation of a code-block, like
this

a, b = [1,7,10,3,12].split do |x|
  x < 10
end

# a = [1,7,3]
# b = [10,12]

I haven't found a function like this (Ruby 1.6.6). Have I missed it?

When trying to implement it, I also found, that there is no Delete_if (it
exists, but does what Delete_if! should be doing). I came up with the
following, can anybody help me, which implementation to use (performance?):

def split1(aArray)
  a = aArray.dup.delete_if do |x|
    not yield x
  end
  aArray.delete_if do |x|
    yield x
  end
  [a, aArray]
end

def split2(aArray)
  a = aArray.dup.delete_if do |x|
    not yield x
  end
  [a, aArray - a]
end

def split3(aArray)
  a = []
  b = []
  aArray.each do |x|
    if yield x then
      a.push x
    else
      b.push x
    end
  end
  [a, b]
end

[method(:split1), method(:split2), method(:split3)].each do |split|
  a,b = split.call([1,7,10,3,12]) do |x|
    x < 10
  end
  p split
  puts "Here goes a: #{a.inspect}"
  puts "Here goes b: #{b.inspect}"
end