From: Josh Cheek <josh.cheek@...>
Date: 2011-07-24T23:16:53+09:00
Subject: Re: best style for setting items in a collection

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On Sat, Jul 23, 2011 at 8:41 PM, Marshall Farrier
<info@marshallfarrier.com>wrote:

> I've only recently started learning Ruby and notice in Thomas'
> Programming Ruby 1.9 that it seems to be stylistically preferable (and
> presumably also faster fwiw) not to use a for loop but rather to use the
> each method as often as possible. But I'm having trouble using combining
> that with re-assigning values inside an array.
>
> More specifically, consider the following problem: We have an array of
> integers and want the result to be the same as the following for loop:
>
> for i in 1...arr.length
>   arr[i] += arr[i - 1]
> end
>
> Is it stylistically better to use the for loop here or do something like
> this:
>
> 1.upto(arr.length - 1) {|i| arr[i] += arr[i - 1]}
>
> Or is there another way of doing it that is better than both of these? I
> feel like I should be able to do this using the each method but can't
> figure out how to make the assignment work that way, and the upto
> version is pretty short and sweet.
>
> --
> Posted via http://www.ruby-forum.com/.
>
>
It's hard to know how to answer this because you're overwriting the values
of indexes that you use in calculations later on. This seems like it is
probably unintentional: If arr was [1,1,1], then are you expecting [1,2,2]
-- the value at index 2 is calculated based on the original value at index
1. Or are you expecting [1,2,3] -- the value at index 2 is calculated based
on the new value at index 1?

If the former, then this is equivalent:
arr.each_cons(2).with_index(1) do |(left, right), index|
  arr[index] = left + right
end


If the latter, then this is equivalent:
(1...arr.length).each { |index| arr[index] += arr[index-1] }

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