From: Rick DeNatale <rick.denatale@...>
Date: 2009-06-08T00:31:36+09:00
Subject: Re: adding, multiplying array

On Sun, Jun 7, 2009 at 10:15 AM, Haris
Bogdanović<haris.bogdanovic@gmail.com> wrote:
> Hi.
>
> I want to multply all elements of two arrays and add that to all elements of
> the third array like this:
>
> c+=a*b
>
> c=[1,1,1]
> a=[2,2,2]
> b=[3,3,3]
>
> c=[7,7,7]  # (1+2*3)=7
>
> I tried (found on google):
>
> a.zip(b).map {|i,j| i*j} (don't really know how that works)

zip weaves two enumerables together and creates a new enumerable:

a.zip(b) # => [[2, 3], [2, 3], [2, 3]]

[[2, 3], [2, 3], [2, 3]].map {|i,j| i*j}

takes each sub-array, multiplies the two elements and returns a new
array with the products which produces [6, 6, 6]

>
> and how to add that to c array ?
>

Just use zip and map again with a block  which adds the elements.

c = c.zip(a.zip(b).map {|i, j| i*j}).map {|i, j|i + j}

Which changes the variable c to reference a new array which turns out
to be [7, 7, 7]
-- 
Rick DeNatale

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