From: Joel VanderWerf <vjoel@...>
Date: 2008-09-11T04:45:02+09:00
Subject: Re: How to operate on 2 arrays simultaneously?

ara.t.howard wrote:
> 
> On Sep 10, 2008, at 1:03 PM, matt neuburg wrote:
> 
>> Everything in Ruby is a pointer. If a[0] is a pointer to a "big long
>> string", then a.zip(b)[0][0] is a pointer to the very same "big long
>> string" - not a copy of the string. So creating the "huge_new_array"
>> just creates some new pointers, right? And pointers are very small. So
>> for huge_new_array to be a problem, the existence of a and b would have
>> to have been problematic to start with - meaning that they would have to
>> have huge length. The amount of *data* in the story (stuff like "big
>> long string") is not increased.
> 
> not really
> 
> 
> cfp:~ > cat a.rb
> mb = 2 ** 20
> 
> big = 2 * mb
> 
> a = Array.new big
> b = a.dup
> 
> memory_usage = `ps -o rss= -p #{Process.pid}`.to_i
> puts memory_usage
> 
> a.zip(b)
> 
> memory_usage = `ps -o rss= -p #{Process.pid}`.to_i
> puts memory_usage

It's less dramatic when the entries are not nil (or fixnum etc)--I think 
that's Matt's point.

mb = 2 ** 20

big = 2 * mb

a = Array.new big do |i| "the string for entry #{i}" end
b = a.dup

memory_usage = `ps -o rss= -p #{Process.pid}`.to_i
puts memory_usage

a.zip(b)

memory_usage = `ps -o rss= -p #{Process.pid}`.to_i
puts memory_usage

__END__
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       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407