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count subset of chars in a line

by GrandFather (Sage)
on Jun 22, 2005 at 03:36 UTC ( #468897=snippet: print w/replies, xml ) Need Help??

Count all occurrences of characters from a given set in a string.

In the code below $CharSet is the set of characters to count. $SearchStr is the string to count them in.

my $Set = qr/[^$CharSet]/;
length join "", split $Set, $SearchStr;

Wrapped up in a rather more general sub:

sub CountSetChars
  my $Count;
  my $CharSet = shift;
  my $Set = qr/[^$CharSet]/;
  my $Param;

  while ($Param = shift)
    if (defined @$Param)
      {map {$Count += CountSetChars ($CharSet, $_)} @$Param;}
    elsif (ref $Param)
      {$Count += length join "", split $Set, @$Param;}
      {$Count += length join "", split $Set, $Param;}
  return $Count;
Replies are listed 'Best First'.
Re: count subset of chars in a line
by Zaxo (Archbishop) on Jun 22, 2005 at 03:49 UTC

    There's a very pretty way to count them with the tr// operator, my $vowel_count = tr/AEIOUYaeiouy//;
    If you want the character list in a variable, you need to string-eval:  my $foo_count = eval "tr/$foo//";

    After Compline,

      Argh, I knew I'd seen a tidy way to do it somewhere. Sorting out the parameter handling for the sub was good exercise though :-).

      Perl is Huffman encoded by design.
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[Lady_Aleena]: tobyink, I did after I failed to get the BLOCK to work. I can't seem to get my brain around grep BLOCK, though I'm okay with grep EXPR.
[shmem]: so in the second example grep returns all true elements of the list passed
[Lady_Aleena]: Okay, so grep BLOCK is not like map BLOCK where something might need to be returned at the end.
[tobyink]: grep { $_ =~ /.*$in.*/; } @my_modules should work just fine. The problem is that you were adding on ;$_ at the end of the block. Why were you doing that?
[Lady_Aleena]: tobyink, I was thinking map.
[tobyink]: Something does need to be returned at the end not $_ though. You need to return (something that will be evaluated as) a boolean.
[Lady_Aleena]: Here is a longish map I did in the same script. my @my_modules = map { my $file = $_; $file =~ s/$module_director y(.+)\.pm/$1/; $file =~ s/\//::/g; $file; } @files;
[Lady_Aleena]: I spent half an hour trying to figure out why map was rewriting @files.
[tobyink]: If you like map you can do map { ($_ =~ /.*$in.*/) ? $_ : () } @my_modules and it will work just the same. grep is neater though.
[Lady_Aleena]: tobyink, I'll keep the grep as is. Thanks everyone!

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