array of arrays or not

coldy has asked for the wisdom of the Perl Monks concerning the following question:

I have two arrays, representing start and stop positions for a sequence,

@a=(1,15,30,50,65)
@b=(5,20,37,55,77)
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so for example, the first elements of each array (1 and 5) represent the numbers 1,2,3,4,5; the two arrays define the numbers 1,2,3,..5,15,16,..,20,...,65,66,...,77) Now, I also have two scalars, say, $s1=9, $s2=35, where these also represent a range of integers 9,10,11,..,35. The problem is to find the numbers defined by @a and @b which intersect with the range defined by $s1 and $s2.

I tend to things the long way in perl, so I thought of creating an array of arrays

 @AoA=([1,5],[15,20],...,[65,77]) <p>
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then finding the intersection of ($s1..$s2) with each of the array elements.

If anybody can think of a better way to do this, any help much appreciated, otherwise, a good way to create the array of array would also be appreciated.

Thanks in advance!

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Re: array of arrays or not by BrowserUk (Patriarch) on Feb 23, 2009 at 07:21 UTC
It's one reasonably efficient line using the data as you currently have it: `#! perl -slw use strict; my @a = ( 1, 15, 30, 50, 65 ); my @b = ( 5, 20, 37, 55, 77 ); my( $s1, $s2 ) =( 9, 35 ); my @result = map{ grep $_ >= $s1 && $_ <= $s2, $a[ $_ ] .. $b[ $_ ] } 0 .. $#a; print "@result"; __END__ C:\test>junk12 15 16 17 18 19 20 30 31 32 33 34 35` [download] Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply] [d/l]
Re: array of arrays or not by ysth (Canon) on Feb 23, 2009 at 07:45 UTC
It's pretty easy as is: `use List::Util qw/max min/; my @result = map max($s1,$a[$_])..min($s2,$b[$_]), 0..$#a;` [download] and only slightly different using an AoA: `my @result = map max($s1,$_->[0])..min($s2,$_->[1]), @AoA;` [download] -- Online Fortune Cookie Search Office Space merchandise	[reply] [d/l] [select]
Re: array of arrays or not by tilly (Archbishop) on Feb 23, 2009 at 07:57 UTC
If your intervals are potentially long, then I'd suggest the array of array approach because it avoids constructing long lists of elements. You can produce that array of arrays with: `my @interval_arrays = map [$a[$_], $b[$_]], 0..$#a;` [download] And then you can intersect with your interval and get a result in the same format with: `my @intersected_arrays = map { my $min = $s1 < $_->[0] ? $_->[0] : $s1; my $max = $s2 > $_->[1] ? $_->[1] : $s2; $min <= $max ? [$min, $max] : (); } @interval_arrays;` [download]	[reply] [d/l] [select]
Re: array of arrays or not by CountZero (Bishop) on Feb 23, 2009 at 09:51 UTC
Perhaps a module such as Number::Interval, Set::Window or Set::IntRange can assist. CountZero A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James	[reply]
Re: array of arrays or not by poolpi (Hermit) on Feb 23, 2009 at 10:51 UTC
`#!/usr/bin/perl use strict; use warnings; use Set::IntSpan; use Data::Dumper; my $set1 = new Set::IntSpan "1-5, 15-20, 30-35, 50-55, 65-70"; my $set2 = new Set::IntSpan "9-35"; my $i_set = $set2 * $set1; my $inter = elements $i_set; print Dumper $inter; __END__ Output: ------ $VAR1 = [ 15, 16, 17, 18, 19, 20, 30, 31, 32, 33, 34, 35 ];` [download] hth, PooLpi 'Ebry haffa hoe hab im tik a bush'. Jamaican proverb	[reply] [d/l]