From: dblack@...
Date: 2006-05-21T11:56:46+09:00
Subject: Re: rubynuby - confused by method name "inject"

Hi --

On Sun, 21 May 2006, Jeff Pritchard wrote:

> Can anybody explain to me how the Enumberable#inject method is
> "injecting" something into something?  I find it very difficult remember
> method names when I don't "get" them.  So far in Ruby, "inject" takes
> the cake for least understandable method name (with my own particular
> convoluted gray matter).
>
> Can somebody give some examples of its use and state in words how it is
> "injecting" something into something?
>
> thanks,
> jp
>
> P.S.
> If anybody wants to take a stab at "collect", that would be welcome
> also.

I have just about the mental energy for collect right now, so I'll
give that a try :-)

The basic usage (just to have an example):

You have an array:  [1,2,3,4,5]
You call:  new_array = array.collect {|element| element * 10 }
The result (new_array) is: [10,20,30,40,50]

Now, in terms of the word "collect" itself:

Imagine that the elements of the first array are sitting on a bus.
The conductor comes through the bus and *collects* the fare from each
element.  The fare is: yourself times 10.  The cumulative result is a
new array, consisting of the old array's elements but each multiplied
by 10.

So collect is an iterative process, where a new value is "collected"
from each old value, courtesy of being passed to the code block.  The
new array is thus a one-to-one mapping of the old array, with the
values transformed.  (So collect is also called "map" :-)


David

-- 
David A. Black (dblack@wobblini.net)
* Ruby Power and Light, LLC (http://www.rubypowerandlight.com)
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* Author of "Ruby for Rails" from Manning Publications!
   > http://www.manning.com/black