From: poopdeville@...
Date: 2006-10-26T05:40:19+09:00
Subject: Premature Optimization

Hi everybody,

I'm writing a fairly open-ended question.  I'm hoping for suggestions,
opinions, advice.  Suppose I have n arrays, each of which has m
entries.  m is a fairly large integer, on the order of 10,000.  Each
entry is either 1 or 0.

The first task I need to accomplish is figuring out how many times a 1
occurs in the ith entry in an array.  So for concreteness, if I had
arrays:

first = [1,0,0,0,0]
second = [1,1,0,0,0]
third = [0,0,0,1,0]

I would end up with
count = [2,1,0,1,0]

I'm just trying to give the general flavor of what I'm working on.  I
know I can use some simple each_with_index loops to increment
count[index] (something along the lines of:)

count = Array.new(m,0)
[first, second, third].each do |array|
  array.each_with_index do |item, index|
    count[index] += item
  end
end

There are going to be m * 3n * (two constant multipliers for the
looping) object allocations and method calls.  m is fairly large, and I
have other, similar, tasks to accomplish with this data.  The faster I
can process this data, the more data I can process in a given amount of
time, and the more accurate the analysis will be.

Is there a slick way to do this with unpacking and packing?  Or some
other way to do this with strings?  Any modules or libraries I should
look into?  I'm fairly new to Ruby, though not to scientific
computation.  I realize I won't be able to do this any faster than with
m * n * (a constant multiplier), but I need that constant multiplier to
be as small as possible.  Any advice would be appreciated.

Thanks!
'cid 'ooh