Problem in "index" function in recognizing repeating substrings

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

Most revered monks,
The built-in index function seems to be able to recognize only the first substring given two identical substrings from a string. My code below:

#!/usr/bin/perl -w
use strict;

my $str = 'NNNNNATCGNNNNATCG';
my @substr  = qw(ATCG ATCG);
foreach (@substr)
{
   my $id = index($str,$_);
   print "$id\n"; 
}
[download]

Returns:

5
5
[download]

How can I overcome this problem such that the index function can recognize the second substrings in the correct position? Returning this instead:

5
13
[download]

Regards,
Edward

Comment on Problem in "index" function in recognizing repeating substrings Select or Download Code

Replies are listed 'Best First'.
Re: Problem in "index" function in recognizing repeating substrings by reasonablekeith (Deacon) on Sep 02, 2005 at 09:47 UTC
`#!/usr/bin/perl -w use strict; my $str = 'NNNNNATCGNNNNATCG'; my @substr = qw(ATCG ATCG); my $id = -1; foreach (@substr) { $id = index($str, $_, $id+1); print "$id\n"; }` [download] --- my name's not Keith, and I'm not reasonable.	[reply] [d/l]
Re: Problem in "index" function in recognizing repeating substrings by Tanalis (Curate) on Sep 02, 2005 at 09:35 UTC
`index` accepts a position to start from as a third argument. If you track `$id` to figure out where in the string you are, you should be able to avoid matching the first instance repeatedly. See the docs for more information. -- Tanalis `#include www.liquidfusion.org.uk`	[reply] [d/l] [select]
Re: Problem in "index" function in recognizing repeating substrings by ysth (Canon) on Sep 02, 2005 at 12:00 UTC
Do you want: `my $str = "ATCGATCGAT"; my @substr = qw(ATCG CGAT);` [download] to give 0 and 2 or 0 and 6? If the latter, do `$id = -1; foreach (@substr) { my $id = index($str,$_,$id); print "$id\n"; $id += length($_); }` [download]	[reply] [d/l] [select]
Re^2: Problem in "index" function in recognizing repeating substrings by reasonablekeith (Deacon) on Sep 02, 2005 at 14:29 UTC
I've pointed this out to him before, didn't get a response then either. --- my name's not Keith, and I'm not reasonable.	[reply]
Re^2: Problem in "index" function in recognizing repeating substrings by monkfan (Curate) on Sep 02, 2005 at 14:52 UTC
Dear ysth, Thanks a lot for pointing out the important case that I missed. With your example above, I will opt for the 'closest' substrings namely: `0 and 2` [download] If the latter You mean the 'former'? Because, having tested your above code, I think it already gave that answer.. Please correct me if I'm wrong. Regards, Edward	[reply] [d/l]
Re^3: Problem in "index" function in recognizing repeating substrings by saberworks (Curate) on Sep 02, 2005 at 16:05 UTC
No, his code clearly gives 0 and 6. If you want 0 and 2, try this: `#!/usr/bin/perl use strict; my $str = 'ATCGATCGAT'; my @sub = qw(ATCG CGAT); my $id = 0; foreach (@sub) { $id = index($str, $_, $id); print "$id\n"; $id++; }` [download]	[reply] [d/l]


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