More efficient comparing

ruby-talk
1

Hello,

I've got an array that holds urls. Example Element:
http://bla.random.com/bla.jpg.

I also have images in a directory. I'd like my script to compare the
bla.jpg from the URL with all files in a directory to make sure it's not
a duplicate of something that's already there - if it is - delete it
from the array. My current way of doing it uses quite a bit of
resources, was wondering if someone could show me a more efficient
example if possible.

Current Code:
Dir["#{$baseDir}/#{board}/#{$dateString}/**"].each do |file|
      $imgArray.delete_if{
        >i> i =~ /#{file.split('/').pop}/
      }

···

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2

1. use file.split('/').last instead of pop - pop modifies the array

2. move the regex out of the block - you'll save some object
constructions/destructions, and it'll be easier on GC too.

3. try instead of splitting using a regex or rindex.
i.e. last_part = $1 if file =~ /\/([^/]*)$/
or last_part = file[file.rindex('/')..-1] or
file[(file.rindex('/')||0)..-1] to fix the cae when there's no '/' in
the filename.

4. use Benchmark class to measure your improvements - that way, you'll
know exactly if the new code is better or not.

···

On Thu, Feb 21, 2008 at 11:24 PM, Kyle Hunter <keletmaster@gmail.com> wrote:

Hello,

I've got an array that holds urls. Example Element:
http://bla.random.com/bla.jpg\.

I also have images in a directory. I'd like my script to compare the
bla.jpg from the URL with all files in a directory to make sure it's not
a duplicate of something that's already there - if it is - delete it
from the array. My current way of doing it uses quite a bit of
resources, was wondering if someone could show me a more efficient
example if possible.

Current Code:
Dir["#{$baseDir}/#{board}/#{$dateString}/**"].each do |file|
      $imgArray.delete_if{
        >i> i =~ /#{file.split('/').pop}/
      }

3

Kyle Hunter wrote:

Hello,

I've got an array that holds urls. Example Element:
http://bla.random.com/bla.jpg\.

I also have images in a directory. I'd like my script to compare the
bla.jpg from the URL with all files in a directory to make sure it's not
a duplicate of something that's already there - if it is - delete it
from the array. My current way of doing it uses quite a bit of
resources, was wondering if someone could show me a more efficient
example if possible.

Current Code:
Dir["#{$baseDir}/#{board}/#{$dateString}/**"].each do |file|
      $imgArray.delete_if{
        >i> i =~ /#{file.split('/').pop}/
      }
  
Try:

require 'set'

files = Dir["#{$baseDir}/#{board}/#{$dateString}/**"].map { |file| File.basename(file) }.to_set

$imgArray.delete_if {|i| files.include? i.split("/")[-1] }

-Justin

4

Thanks both of you,

Justin's example seems to have made it more efficient. Later on I'll
compare my original, a version with Jano's suggestions, and Justin's
using benchmark to see what is the most efficient.

Any more suggestions are welcome, of course, the more to benchmark the
merrier!

···

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