Split array into smaller arrays of equal size

mattsa (Matt Sanders) — Fri, 09 Feb 2007 22:52:07 GMT

Split an array of elements into a set of smaller arrays of equal size. Extra elements are preferentially assigned to earlier arrays. If there are no elements in a given returned array it will be [] (empty array)



# use as standalone function

def chunk_array(array, pieces=2)

  len = array.length;

  mid = (len/pieces)

  chunks = []

  start = 0

  1.upto(pieces) do |i|

    last = start+mid

    last = last-1 unless len%pieces >= i

    chunks << array[start..last] || []

    start = last+1

  end

  chunks

end



# use as array.chunk

class Array

  def chunk(pieces=2)

    len = self.length;

    mid = (len/pieces)

    chunks = []

    start = 0

    1.upto(pieces) do |i|

      last = start+mid

      last = last-1 unless len%pieces >= i

      chunks << self[start..last] || []

      start = last+1

    end

    chunks

  end

end

Examples of use:



>> chunk_array [1,2,3,4,5,6], 2

=> [[1, 2, 3], [4, 5, 6]]



>> chunk_array [1,2,3,4,5,6], 3

=> [[1, 2], [3, 4], [5, 6]]



>> chunk_array [1,2,3,4,5,6], 4

=> [[1, 2], [3, 4], [5], [6]]



>> chunk_array [1,2,3,4,5,6,7,8,9,10], 4

=> [[1, 2, 3], [4, 5, 6], [7, 8], [9, 10]]



>> chunk_array [1,2,3], 4

=> [[1], [2], [3], []]



>> chunk_array [], 2

=> [[], []]

if you prefer the second form (more ruby-ish, but not always appropriate)



>> [1,2,3,4,5,6,7,8,9,10].chunk

=> [[1, 2, 3, 4, 5], [6, 7, 8, 9, 10]]



>> [1,2,3,4,5,6,7,8,9,10].chunk 3

=> [[1, 2, 3, 4], [5, 6, 7], [8, 9, 10]]

This is handy when used with a splat because you can do things like:



left, right = *chunk_array(all,2)

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Split array into smaller arrays of equal size