DZone Snippets: chunk code

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)

Database connection chunk

plasticated () — Tue, 05 Dec 2006 21:53:19 GMT



mysql_select_db($database_conname, $conname);



$query_name = "SELECT * FROM tablename ORDER BY column DESC LIMIT 0, 10";

$name = mysql_query($query_name, $conname) or die(mysql_error());

$row_name = mysql_fetch_assoc($conname);

$totalrows_name = mysql_num_rows($conname);

Split String into roughly equal-sized chunks.

duncanbeevers (Duncan Beevers) — Thu, 21 Sep 2006 00:29:28 GMT

Split a string into an array of roughly equal sized chunks based on a string or regular expression delimiter.
Delimiter is preserved in output.



class String

  def chunk_string(average_segment_size = 40, sclice_on = /\s+/)

    out = []

    slices_estimate = self.size.divmod(average_segment_size)

    slice_count = (slices_estimate[1] > 0 ? slices_estimate[0] + 1 : slices_estimate[0])

    slice_guess = self.size / slice_count

    previous_slice_location = 0

    (1..slice_count - 1).each do

      |i|

      slice_location = self.nearest_split(slice_guess * i, sclice_on)

      out << self.slice(previous_slice_location..slice_location)

      previous_slice_location = slice_location + 1

    end

    out << self.slice(previous_slice_location..self.size)

    out

  end



  def nearest_split(slice_start, slice_on)

    left_scan_location  = (self.slice(0..slice_start).rindex(slice_on)).to_i

    right_scan_location = (self.slice((slice_start+1)..self.size).index(slice_on)).to_i + slice_start

    ((slice_start - left_scan_location) < (right_scan_location - slice_start) ? left_scan_location : right_scan_location)

  end

end

chunk function

gregg.irwin (Gregg Irwin) — Tue, 10 Jan 2006 06:20:13 GMT



    split: chunk: segment: func [  ; subdivide ?

        {See: CLOS pg. 937. Not that mine works the same, but that was

        the inspiration.}

        series [series!]

        size   [integer!] "The size of the chunks (last chunk may be shorter)"

        /into  "split into a set number (size) of chunks (last chunk may be longer than others)."

        /local ct cur-piece result

    ][

        ct: either into [size] [round/down divide length? series size]

        if into [size: to-integer divide length? series size]

        result: copy []

        if zero? size [return result]

        parse series [

            ct [

                copy cur-piece size skip (append/only result cur-piece) mark:

            ]

        ]

        if any [into  not zero? remainder length? series size] [

            cur-piece: copy mark

            either into

                [append last result cur-piece]

                [append/only result cur-piece]

        ]

        result

    ]