Multiple Transformations with "map"

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

Why my code below:

$ perl -MData::Dumper -e '
@arr = ("A[TCG]GG 3", "CTG[AA] 4");
@nar = map {  #get rid of trailing number 
              my $st = (split(" ",$_))[0];

              #replace bracket with S
              $st =~ s/\[[ATCG]+\]/S/g; } @arr; 
print Dumper \@nar
'
[download]

doesn't produce this:

$VAR1 = [
          'ASGG',
          'CTGS'
        ];
[download]

Regards,
Edward

Comment on Multiple Transformations with "map" Select or Download Code

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Re: Multiple Transformations with "map" by davido (Cardinal) on Nov 26, 2005 at 07:43 UTC
map returns the value of the last expression evaluated within `{ #block }`. The last expression you're evaluating is a substitution operator, and its value is a boolean value; true (1) if a match occurred, or false if there was no match. That's why it keeps passing '1' into @nar. If you want to return the result of the substitution, make sure that value is the last thing evaluated in `{ #block }`. `@nar = map { # get rid of trailing number my $st = ( split( " ", $_ ) )[0]; # replace bracket with S $st =~ s/\[[ATCG]+\/S/g; # return result value $st; } @arr;` [download] ...that ought to do it... Dave	[reply] [d/l] [select]
Re^2: Multiple Transformations with "map" by sauoq (Abbot) on Nov 26, 2005 at 13:06 UTC
The last expression you're evaluating is a substitution operator, and its value is a boolean value; true (1) if a match occurred, or false if there was no match. If a match occurs, the substitution operator returns the number of substitutions made, not simply 1 (unless that happens to be the number of substitutions made... as in this case.) -sauoq "My two cents aren't worth a dime.";	[reply]
Re: Multiple Transformations with "map" by TedPride (Priest) on Nov 26, 2005 at 15:15 UTC
I personally never liked map. for works just as well in almost all situations, and it's much easier to understand. `my @arr = ("A[TCG]GG 3", "CTG[AA] 4"); for (@arr) { s/ .*//; s/\[[ATCG]+\]/S/g; } print join "\n", @arr;` [download]	[reply] [d/l]