use strict;
use warnings;

my %hash;

while (<DATA>)
{
    if ( /(\w) (.+)/ )
    {
        $hash{$1} .= $2;
    }
}
for ( sort keys %hash )
{
    print "$_ $hash{$_}\n";
}
__DATA__
A A_
B B_
C C_
D D_
E E_
A A*
B B*
C C*
D D*
E E*
A A-
B B-
C C-
D D-
E E-
A AB
B BB
C CC
D DD
[download]

A A_A*A-AB
B B_B*B-BB
C C_C*C-CC
D D_D*D-DD
E E_E*E-
[download]

What happened to A*, B*, C*, etc?

Perhaps you want something like this:

# Use strict and warnings, etc
# Read the file and hash it
my %data;
while (<>) {
  my ($k, $v) = split /\t/; # Split on tabs
  my $values= $data{$k} ||= []; # ensure we have an array ref
  push @$values, $v;  # add the value to the end of list for this key
}

# Print out the results
for (sort keys %file) { # Sort is optional
  print join "\t", ($_, @{ $data{$_} }); # Assuming you want them tab 
+seperated
  print "\n";
}
[download]

Code is untested...

#!perl -w
use strict;
my %hash;
for my $line(<DATA>) {
    chomp($line);
    my($key,$val) = split /\t/, $line;
    next unless defined $key and defined $val;
    $hash{$key} .= " $val";
}
print $hash{$_} . "\n" for keys %hash;
__DATA__
A    A_
B    B_
C    C_
D    D_
E    E_
A    A*
B    B*
C    C*
D    D*
E    E*
A    A-
B    B-
C    C-
D    D-
E    E-
A    AB
B    BB
C    CC
D    DD
[download]

If your data is "tab delimited" and you have 300mb of it, you can use Text::CSV_XS, the fastest method of parsing "delimited" data (which is really "separated" data). Just start the module with sep_char="\t" and it will handle your data fine.

$file =
'0.000000e+000 1.502947e+000
1.162272e-012 1.508957e+001
2.324544e-012 1.508948e+000';

my $regex = {
 'first'  => qr{^(\S+)},  # anything non-blank from the beginning '^'
 'second' => qr{\s+(\S*)} # anything non-blank after the fist blank '\
+s+'
};

for(split '\n', $file){
 /$regex->{first}$regex->{second}/o # 'o' compiles the regex
 and # and upon success we take the first column and/or the second one
 print "Key: $1 and Value: $2\n";
 # So hash structure can have $hash{$1} = $2
}
[download]

Hi sh1n,

are we assigning these lines
'0.000000e+000 1.502947e+000
1.162272e-012 1.508957e+001
2.324544e-012 1.508948e+000';
to the variable $file. With '...' in the middle means some 2000 more pairs in continuity. Kindly explain your very first line of the code.
many thanks,
riz.

I wouldn't try to pattern match the scientific float... you could, but I think it's over-kill. If the data is tab delimited, then you can use that to distinguish the two values:

use strict;
while(<DATA>)
{
  # Get rid of trailing \n on line.
  chomp;

  # divide the line into two items based on tab
  my ($x, $y) = split("\t");    
  print "X:[$x]  Y: [$y]\n";
}

##OUTPUT:
# X:[0.000000e+000]  Y: [1.502947e+000]
# X:[1.162272e-012]  Y: [1.508957e+001]
# X:[2.324544e-012]  Y: [1.508948e+000]
# X:[0.000000e+000]  Y: [1.502947e+001]
# X:[1.162272e-012]  Y: [1.508941e+001]
# X:[2.324544e-012]  Y: [1.508940e+000]
# X:[0.000000e+000]  Y: [1.503947e+000]
# X:[1.162272e-012]  Y: [1.504947e+000]
# X:[2.324544e-012]  Y: [1.508900e+001]

##NOTE in data the two fields are tab delimited.

__DATA__
0.000000e+000    1.502947e+000
1.162272e-012    1.508957e+001
2.324544e-012    1.508948e+000
0.000000e+000    1.502947e+001
1.162272e-012    1.508941e+001
2.324544e-012    1.508940e+000
0.000000e+000    1.503947e+000
1.162272e-012    1.504947e+000
2.324544e-012    1.508900e+001
[download]

---

"Look, Shiny Things!" is not a better business strategy than compatibility and reuse.

wouldn't try to pattern match the scientific float... you could, but I think it's over-kill.

Do you really have any idea what does  /^(\S+)\s+(\S*)/o do?



/^(\S+)\s+(\S*)/o and print FH "K: ", $1, "V: ", $2, "\n" while <DATA>
+;
[download]



where <DATA> contains over 22000 lines - less than a second
on my old (less than 1800 Mh cpu) home machine.