Re: How to call a function on each item after a split?

Hi,

Please, before one shutdown the wonderful solution first given by aitap above on this issue,
Or wonder why "the" lovely map function doesn't do the "magic" as expected, Please, check the OP subroutine clean().

sub clean
{
    chomp($_[0]);
    $_[0] =~ s/^\s+//g;
    $_[0] =~ s/\s+$//g;
}
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Why use chomp and then sepeartely, remove spaces? At the beginning and endling of each value?
I thought, \s+ also covers \n that chomp is suppose to remove?
I modified the OP clean subroutine and both map and grep gave the happy endling.
So, there is really no need for the extra $_ as perviously stated, if the modified subroutine is considered.
check below:

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

my $str = "item1  | item2| item3 
|item4|
 ";

my @cleaned1 = map { clean_modify($_) } split( /\|/, $str );
my @cleaned2 = grep { clean_modify($_) } split( /\|/, $str );

print join "\n", @cleaned1;
print join "\n", @cleaned2;

sub clean_modify {
    $_[0] =~ s/^\s+?|\s+?$//g;
    return $_[0];
}

sub clean {  ## don't use
    chomp( $_[0] );
    $_[0] =~ s/^\s+//g;
    $_[0] =~ s/\s+$//g;
}
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OUTPUT

item1
item2
item3
item4
item1
item2
item3
item4
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If you tell me, I'll forget.
If you show me, I'll remember.
if you involve me, I'll understand.
--- Author unknown to me

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Re^2: How to call a function on each item after a split? by Lotus1 (Vicar) on Oct 10, 2012 at 02:40 UTC
Your demonstration of using grep like that only works if the function modifies $_. Your example makes it seem that map and grep are equivalent which they aren't. grep looks at the return value in the block to determine whether or not to pass along $_ while map passes along the return value in the block. Big difference. If one of the values in the string happens to be '0' then grep doesn't pass that value through. Also your solution doesn't pass along the final empty string like the one with the `map{ clean($_);$_ }` solution did. #!/usr/bin/perl use strict; use warnings; my $str = "item1 \| 0 \| \| item2\| item3 \|item4 \| "; my @cleaned1 = map { clean_no_side_effects($_) } split( /\\|/, $str ); my @cleaned2 = grep { clean_no_side_effects($_) } split( /\\|/, $str ); print ""x25, "\n"; print join "\n", @cleaned1; print ""x25, "\n"; print join "\n", @cleaned2; print ""x25, "\n"; sub clean_no_side_effects { my $string = shift; $string =~ s/^\s+\|\s+$//g; return $string; } sub clean_modify { ## don't use, still using side effects for grep t +o work $_[0] =~ s/^\s+?\|\s+?$//g; # '?' isn't needed here since \s neve +r matches '\|' return $_[0]; } sub clean { ## don't use chomp( $_[0] ); $_[0] =~ s/^\s+//g; $_[0] =~ s/\s+$//g; } __END__ ********************** item1 0 item2 item3 item4 ********************* item1 item2 item3 item4 *********************** [download]	[reply] [d/l] [select]

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Re^2: How to call a function on each item after a split?
by Lotus1 (Vicar) on Oct 10, 2012 at 02:40 UTC

Your demonstration of using grep like that only works if the function modifies $_. Your example makes it seem that map and grep are equivalent which they aren't. grep looks at the return value in the block to determine whether or not to pass along $_ while map passes along the return value in the block. Big difference. If one of the values in the string happens to be '0' then grep doesn't pass that value through. Also your solution doesn't pass along the final empty string like the one with the map{ clean($_);$_ } solution did.

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

my $str = "item1 | 0 |  |   item2| item3 
|item4 
 |
 ";

my @cleaned1 = map { clean_no_side_effects($_) } split( /\|/, $str );
my @cleaned2 = grep { clean_no_side_effects($_) } split( /\|/, $str );

print "*"x25, "\n";
print join "\n", @cleaned1;
print "*"x25, "\n";
print join "\n", @cleaned2;
print "*"x25, "\n";

sub clean_no_side_effects {  
    my $string = shift;
    $string =~ s/^\s+|\s+$//g;
    return $string;
}

sub clean_modify {   ## don't use, still using side effects for grep t
+o work
    $_[0] =~ s/^\s+?|\s+?$//g;   # '?' isn't needed here since \s neve
+r matches '|'
    return $_[0];
}

sub clean {  ## don't use
    chomp( $_[0] );
    $_[0] =~ s/^\s+//g;
    $_[0] =~ s/\s+$//g;
}
__END__
*************************
item1
0

item2
item3
item4
*************************
item1 
   item2
 item3 

item4 
 *************************
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