From: Eric Hodel <drbrain@...7.net>
Date: 2011-07-24T16:57:58+09:00
Subject: Re: best style for setting items in a collection

On Jul 23, 2011, at 6:41 PM, Marshall Farrier 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.

I'm not sure what you're calculating here, but if I wanted to add the items in an Array with one item to the left I would use:

arr.zip(arr.rotate).map { |a, b| a + b }

This doesn't calculate the same result as yours, but I'm not sure exactly what you want to do.