How do I iterate through an array of nils? - ruby

Question

I'm trying to set up an Array with all nil values so that someone can iterate the sequence for each value until it reaches the end, then displays the changed array.
class Big
def ben
x = [nil,1,nil,2]
y = 0
x[y] == nil ? "good": "bad"
y += 1
puts x
end
end
I know this can be simplified. Is there a way to overwrite each value in the array?

Answer 1

Here are some things that might help, based on what I see in the sample code.
This is a simple way to create an array if you want it to be a certain size filled with nil values:
foo = [nil] * 5
=> [nil, nil, nil, nil, nil]
If you want to interweave two arrays, such as an array of nils and another one with values:
TOTAL_ELEMENTS = 5
([nil] * TOTAL_ELEMENTS).zip((1..TOTAL_ELEMENTS).to_a).flatten
=> [nil, 1, nil, 2, nil, 3, nil, 4, nil, 5]
Based on the OPs comment below, that this is for a tic-tac-toe game, here are some ways to create x:
Array.new(9)
[nil] * 9
Both of which return:
=> [nil, nil, nil, nil, nil, nil, nil, nil, nil]
That is useful if you receive the cell coordinate as an offset from 0.
For a tic-tac-toe grid it might be more useful to have three rows of three columns if you get your cell coordinates as an row/column pair:
Array.new(3) { Array.new(3) }
[[nil] * 3] * 3
Returning:
=> [[nil, nil, nil], [nil, nil, nil], [nil, nil, nil]]
And some things to meditate on:
ROWS = COLUMNS = 3
x = Array.new( ROWS * COLUMNS ) # for offsets
x = Array.new(ROWS) { Array.new(COLUMNS) } # for rows and columns
If you get your position as an offset but want to convert it to a row/column,
use divmod. Your offset will be 0..8, being converted to fit into a 3x3 grid,
i.e. [0..2][0..2]. Converting back is easy too:
def row_col_to_offset(x,y)
x * ROW + y
end
>> row_col_to_offset(0,0) # => 0
>> row_col_to_offset(0,1) # => 1
>> row_col_to_offset(1,1) # => 4
>> row_col_to_offset(2,2) # => 8
def offset_to_row_col(o)
o.divmod(ROW)
end
>> offset_to_row_col(0) # => [0, 0]
>> offset_to_row_col(1) # => [0, 1]
>> offset_to_row_col(4) # => [1, 1]
>> offset_to_row_col(8) # => [2, 2]
Now you need to learn about Ruby's # instance variables, and the proper use of the initialize method.

Answer 2

If I'm understanding you right you could do this:
class Big
def ben
x = [nil,1,nil,2]
# These lines don't do much
# y = 0
# x[y] == nil ? "good": "bad"
# y += 1
puts x
end
end
And yes to your second question: fill. For example:
[1, 2, 3].fill(0) # => [0, 0, 0]