Extracting and inserting a "column" from/into an array

Discussion in 'Ruby' started by Chauk-Mean Proum, Jun 16, 2009.

  1. Hi,

    For image processing, I have to do the following operations :

    1/ I have an array and I want to extract every 4 element into another
    array :

    # r=red, g=green, b=blue, a=alpha
    img_data = [ "r1", "g1", "b1", "a1", "r2, "g2", "b2", "a2" ]

    => [ "a1", "a2" ] # the array of every four elements i.e. alpha data

    It's like extracting the fourth column of a matrix of n rows and 4

    2/ Conversely, I have an array and I need to add elements at every 3

    img_data = [ "r1", "g1", "b1", "r2, "g2", "b2" ]
    alpha_data = [ "a1", "a2" ] # the elements to add

    => [ "r1", "g1", "b1", "a1", "r2, "g2", "b2", "a2" ]

    It's like inserting a column to a matrix of n rows and 3 columns.

    I'm wondering if there is an easy or seamless way to do these
    Thanks in advance for any tips.


    Chauk-Mean Proum, Jun 16, 2009
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  2. Chauk-Mean Proum

    Matt Neuburg Guest

    Array is an Enumerable so when you require 'enumerator' you get a bunch
    of cool ways of slicing it up.
    result = img_data.enum_slice(4).map {|arr| arr[3]}
    result = img_data.enum_slice(3).zip(alpha_data).flatten

    Matt Neuburg, Jun 16, 2009
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  3. Hi Matt,
    This is exactly what I was looking for. I just replace enum_slice with
    each_slice as I'm using ruby 1.9.
    Thanks a lot.


    Chauk-Mean Proum, Jun 16, 2009
  4. Chauk-Mean Proum

    Phrogz Guest

    Possibly not as efficient, but if you were representing the data as a
    '2D' array (array of arrays) alternatively you could .transpose the
    array, insert a row, and .transpose it back.
    Phrogz, Jun 17, 2009
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