From: Eric Hodel <drbrain@...7.net>
Date: 2011-07-25T09:41:27+09:00
Subject: Re: best style for setting items in a collection

On Jul 24, 2011, at 9:25 AM, Marshall Farrier wrote:
> Ok, sorry that my example muddled things so much. I did mean the latter. 
> The point of departure is that arr initially holds the (non-leap-year) 
> number of days in each month with 0 up front for month 0: [0, 31, 28, 
> 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]. Then I want to modify it so 
> that it holds the aggregate days in normal years up to the end of the 
> month in question. I then use this array for various date calculations.

Using each_with_index:

month_lengths = [0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]

total_lengths = [0]

month_lengths.each_with_index do |length, i|
  total_lengths[i] = length + total_lengths[i - 1]
end

p total_lengths

Here's a version using inject:

month_lengths = [0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]

total_lengths = [0]

month_lengths.inject do |length, total|
  total += length
  total_lengths << total
  total
end

p total_lengths