Create two-dimensional arrays and access sub-arrays in Ruby

Question

I wonder if there s a possibility to create a two dimensional array and to quickly access any horizontal or vertical sub array in it    I believe we can access a horizontal sub array in the following case   x   Array new 10    Array new 20     x 6  3  8     something    But as far as I understand  we cannot access it like this   x 3  8  6    How can I avoid or hack this limit

User · Answer

I m quite sure this can be very simple  2 0 0p247  032  gt  list   Array new 5      gt   nil  nil  nil  nil  nil    2 0 0p247  033  gt  list map    x  x    0        gt    0    0    0    0    0     2 0 0p247  034  gt  list 0  0       gt  0

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Here s a 3D array case  class Array3D    def initialize d1 d2 d3       data   Array new d1    Array new d2    Array new d3         end    def    x  y  z       data x  y  z    end    def     x  y  z  value       data x  y  z    value   end end   You can access subsections of each array just like any other Ruby array   data 0  2  3  5  8  10    0  etc

User · Answer

Here is an easy way to create a  2D  array   2 1 1  004  gt  m Array new 3 Array new 3 true      gt    true  true  true    true  true  true    true  true  true

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Here is the simple version    one  a     0  10  10    two row  col   10  10 a     0  row  col

User · Answer

There are some problems with 2 dimensional Arrays the way you implement them   a    1 2   3 4   a 0  2   5   works a 2  0   6   error   Hash as Array  I prefer to use Hashes for multi dimensional Arrays  a  Hash new a  1 2    23 a  5 6    42   This has the advantage  that you don t have to manually create columns or rows  Inserting into hashes is almost O 1   so there is no drawback here  as long as your Hash does not become too big   You can even set a default value for all not specified elements  a  Hash new 0    So now about how to get subarrays   3  5  to a product  2   collect    index  a index     2  product  3  5  to a  collect    index  a index       a  b  to a runs in O n   Retrieving an element from an Hash is almost O 1   so the collect runs in almost O n   There is no way to make it faster than O n   as copying n elements always is O n    Hashes can have problems when they are getting too big  So I would think twice about implementing a multidimensional Array like this  if I knew my amount of data is getting big

User · Answer

rows  cols   x y    your values grid   Array new rows    Array new cols      As for accessing elements  this article is pretty good for step by step way to encapsulate an array in the way you want   How to ruby array

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x transpose 6  3  8  or x 3  8  map   r  r  6   would give what you want   Example   a      1   2   3   4   5          6   7   8   9   10          11  12  13  14  15          21  22  23  24  25          a 1  2  2   - gt   8 13  puts a transpose 2  1  2  inspect      8 13  puts a 1  2  map   r  r 2   inspect     8 13

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a   Array new Array new 4    0 upto a length-1  do  i    0 upto a length-1  do  j      a i j     1   end end  0 upto a length-1  do  i    0 upto a length-1  do  j      print a i j     1  It s not a i  j   but a i j     end   puts   n  end

User · Answer

You didn t state your actual goal  but maybe this can help   require  matrix     bundled with Ruby m   Matrix    1  2  3     4  5  6     m column 0       gt  Vector 1  4     and Vectors acts like arrays   or  using a similar notation as you desire   m minor 0  1  2  2      gt  Matrix  3    6

[ruby] Create two-dimensional arrays and access sub-arrays in Ruby

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