in reply to Re: tr/// statement
in thread tr/// statement

Could you please give me some more help on this tr/// statement?
Could you please tell me if there is any improvement I should do? I use something like this: 
@letter = qw( a b c w x y );
for ($n=0; $n<6; $n++){
$x = $letter[$n];
$m = 0;

open (DATA, "data.txt") ||
die "Could not open source data file.";
while (<DATA>) {
$cnt = eval "tr/$x/$x/";
$m += $cnt;
}

print "$x  $m";
}

[download]
data.txt contains lines like:
aedj dfas jijiojsdf dsfwfy jiox jiohjdfax jojojdjj, oiiia oioje asfdc oujsdfayx soujfosdxjpoiojfdxjljojaois jojojx jopjpx jojoijx joijiodfx

asdfasdf jjalsdf jlajkldf jojiojsd jiojasj ioj wwdn jojae jojocjoc joijss jiojwx jiojoxuiojy joiyu oiuouyy

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Re: A another tr/// statement question..
by kevin_i_orourke (Friar) on Jul 19, 2001 at 16:29 UTC

    This is unrelated to your tr/// problem but I would suggest using:

    foreach $x (@letter) {

    instead of your for loop, that way you don't have to remember to change the loop termination value from 6 if you change the number of letters.

    Kevin O'Rourke

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[d/l]
      Muchas gracias Kevin!
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Re: A another tr/// statement question..
by bwana147 (Pilgrim) on Jul 19, 2001 at 16:55 UTC

    I'd rather not open and close the file more than once: disk accesses take time (there's the cache, you didn't mention your file's size). Instead, I would first generate subs that count a given character and store them in a hash, referenced by that character.

    Then, for each line in the file, loop over the letters and call the sub from the hash. Increment a counter which is itself stored in a hash.

    #!/usr/local/bin/perl
use strict;

my @letter = qw/ a b c x y z /;

my %subs;
my %counts;
foreach ( @letter ) {
  $subs{$_} = eval "sub { \$_[0] =~ tr/$_// }";
}

while ( <DATA> ) {
  foreach my $letter ( @letter ) {
    $counts{$letter} += $subs{$letter}->($_);
  }
}

print "$_: $counts{$_}\n" foreach @letter;

__DATA__
aedj dfas jijiojsdf dsfwfy jiox jiohjdfax jojojdjj, oiiia oioje asfdc 
+oujsdfayx soujfosdxjpoiojfdxjljojaois jojojx jopjpx jojoijx joijiodfx

asdfasdf jjalsdf jlajkldf jojiojsd jiojasj ioj wwdn jojae jojocjoc joi
+jss jiojwx jiojoxuiojy joiyu oiuouyy

    [download]

    --bwana147

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Re: A another tr/// statement question..
by stefan k (Curate) on Jul 19, 2001 at 16:34 UTC
    Hi,
    I'd write the whole thing as: 
    @letter = qw/a b c w x y/;

foreach $x (@letter) {
  $m = 0;
  open(DATA,"data.txt") or die
    "couldn't open data\n$!";
  while (<DATA>) {
    $m += ($_ =~ s/$x/$x/g);
  }
  close(DATA);
  print "count $x = $m\n";  
}

    [download]
    (note the use of foreach, or and $! ...)

    Regards... Stefan

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[d/l]
[select]
      Thank you very much Stefan!
[reply]
Re: A another tr/// statement question..
by runrig (Abbot) on Jul 19, 2001 at 18:46 UTC
    If you just want letter counts, you could do something like this (though I have a hard time believing this is not homework):
    my $letters = "abcwxy";

my $re = qr/[$letters]/;
my $cnt;

while (<INPUT>)
 $cnt++ while /$re/g;
}
print "$cnt\n";

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