How to map over a nested array

Question

I have an array:

my_array = [[1,2,3,4],
            [5,6,7,8],
            [9,10,11,12]]

I want to iterate over each "cell" and change the value to something else. How can I do this without flattening the array and recomposing. Something like:

   my_array.each_with_index do |row, row_index|
      row.each_with_index do |cell, col_index|
        my_array[row_index][col_index] = random_letter
      end
    end

The above method doesn't exactly turn out how I would think (the random letter's work, but each row has the same random letters as the last row, in the same order)

Thoughts?

Solution 1

You don't need indexing at all.

my_array.map{|row| row.map{random_letter}}

If you want to retain the object id of each array and change the content, then you can use replace.

my_array.each{|row| row.replace(row.map{random_letter})}

Solution 2

I think the below will work:

my_array.map{|ar| ar.map{ "random number" } }


my_array = [[1,2,3,4],
        [5,6,7,8],
        [9,10,11,12]]
my_array.map{|ar| ar.map{ rand(100...400) }}
# => [[345, 264, 194, 157], [325, 117, 144, 149], [303, 228, 252, 199]]