Re^4: Proper usage of rindex function?

Yes, sorry, I copied-pasted it from the actual code, hence the two different variable names...
I changed it a bit:

if($str=~/([ATCG])\.+$/)
{
    $last_mapped_char=$1;
    $rightmost_position_of_letter = rindex($str, $last_mapped_char)+1;
}
[download]

and now I think it is more sensible (at least to me). The problem I would have with the solution kindly provided above is that I would always need to compare the 4 values and find the largest one (because I only care about the last found A,T,G or C (does not matter which), before the dots start.

Comment on Re^4: Proper usage of rindex function? Download Code

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Re^5: Proper usage of rindex function? by 1nickt (Canon) on Dec 29, 2017 at 12:54 UTC
If that is your spec, then you should use the special array `@-` to report the position of the match. You don't need `rindex` for this (although it is possible that using `rindex` would be faster, even with the additional step of comparing positions, especially with a long string): `perl -Mstrict -wE ' my $str = "ATCGATCGA..."; if ( $str =~ /([ATCG])\./ ) { say "$1 at $-[1]"; } '` [download] Output: `A at 8` [download] See Variables related to regular expressions in perlvar. Hope this helps! update: simplified the re The way forward always starts with a minimal test.	[reply] [d/l] [select]
Re^6: Proper usage of rindex function? by Anonymous Monk on Dec 29, 2017 at 13:06 UTC
Great! Thank you very much!	[reply]
Re^5: Proper usage of rindex function? by Anonymous Monk on Dec 29, 2017 at 16:35 UTC
That assumes the string ends in a dot; it won't find a letter at the final position. Also, the backtracking on the plus modifier is going to kill performance on long strings. You might want to use something like `reverse($str) =~ /[ATCG]/`.	[reply]
Re^5: Proper usage of rindex function? by Anonymous Monk on Dec 29, 2017 at 21:33 UTC
A regex solution might be fairly efficient, since you are looking for a simple word boundary. But I'd suggest using tr+index if making a copy of the `$str` is not a problem. That might be the fastest as well. `# sub via_rx { $_[0] =~ /.\b(?<=[ATCG])/s; $+[0] } sub via_rx { $_[0] =~ /.\w\b/s; $+[0] } sub via_tr { 1+rindex(($_[0] =~ tr/ATCG/X/r), 'X') }` [download]	[reply] [d/l] [select]