Mixing
perl - how work while loop on this program
I have this code but I don't understand how it works specifically this $counts{$user}{$program}++;
my %counts;
open my $IN, '<', 'SESSION.txt' or die;
while (<$IN>) {
next if length ($_) < 51;
my ($sid, $user, $terminal, $program) = unpack 'A9 @11 A25 @37 A15 @53 A25';
next if $sid eq '---------'; # you need some way to filter out bogus or header rows
$program =~ s/(.+//; # based on your example, turn toto (fifi) into toto
$counts{$user}{$program}++; #how that work ?
}
#close $IN;
while (my ($user, $ref) = each %counts) {
while (my ($program, $count) = each %$ref) {
print "User = $count $user with program $programn";
}
}
perl
edited Jan 2 at 16:31
WhatsThePoint
2,25162139
asked Jan 2 at 14:32
dfg ertdfg ert
95
add a comment |
I have this code but I don't understand how it works specifically this $counts{$user}{$program}++;
my %counts;
open my $IN, '<', 'SESSION.txt' or die;
while (<$IN>) {
next if length ($_) < 51;
my ($sid, $user, $terminal, $program) = unpack 'A9 @11 A25 @37 A15 @53 A25';
next if $sid eq '---------'; # you need some way to filter out bogus or header rows
$program =~ s/(.+//; # based on your example, turn toto (fifi) into toto
$counts{$user}{$program}++; #how that work ?
}
#close $IN;
while (my ($user, $ref) = each %counts) {
while (my ($program, $count) = each %$ref) {
print "User = $count $user with program $programn";
}
}
perl
edited Jan 2 at 16:31
WhatsThePoint
2,25162139
asked Jan 2 at 14:32
dfg ertdfg ert
95
1
Hi and welcome to Stack Overflow, please take a time to go through the welcome tour to know your way around here (and also to earn your first badge), read how to create a Minimal, Complete, and Verifiable example and also check How to Ask Good Questions so you increase your chances to get feedback and useful answers.
– jess
Jan 2 at 14:35
add a comment |
I have this code but I don't understand how it works specifically this $counts{$user}{$program}++;
my %counts;
open my $IN, '<', 'SESSION.txt' or die;
while (<$IN>) {
next if length ($_) < 51;
my ($sid, $user, $terminal, $program) = unpack 'A9 @11 A25 @37 A15 @53 A25';
next if $sid eq '---------'; # you need some way to filter out bogus or header rows
$program =~ s/(.+//; # based on your example, turn toto (fifi) into toto
$counts{$user}{$program}++; #how that work ?
}
#close $IN;
while (my ($user, $ref) = each %counts) {
while (my ($program, $count) = each %$ref) {
print "User = $count $user with program $programn";
}
}
perl
edited Jan 2 at 16:31
WhatsThePoint
2,25162139
asked Jan 2 at 14:32
dfg ertdfg ert
95
I have this code but I don't understand how it works specifically this $counts{$user}{$program}++;
my %counts;
open my $IN, '<', 'SESSION.txt' or die;
while (<$IN>) {
next if length ($_) < 51;
my ($sid, $user, $terminal, $program) = unpack 'A9 @11 A25 @37 A15 @53 A25';
next if $sid eq '---------'; # you need some way to filter out bogus or header rows
$program =~ s/(.+//; # based on your example, turn toto (fifi) into toto
$counts{$user}{$program}++; #how that work ?
}
#close $IN;
while (my ($user, $ref) = each %counts) {
while (my ($program, $count) = each %$ref) {
print "User = $count $user with program $programn";
}
}
perl
perl
edited Jan 2 at 16:31
WhatsThePoint
2,25162139
asked Jan 2 at 14:32
dfg ertdfg ert
95
edited Jan 2 at 16:31
WhatsThePoint
2,25162139
asked Jan 2 at 14:32
dfg ertdfg ert
95
edited Jan 2 at 16:31
WhatsThePoint
2,25162139
edited Jan 2 at 16:31
WhatsThePoint
2,25162139
edited Jan 2 at 16:31
WhatsThePoint
2,25162139
2,25162139
asked Jan 2 at 14:32
dfg ertdfg ert
95
asked Jan 2 at 14:32
dfg ertdfg ert
95
asked Jan 2 at 14:32
dfg ertdfg ert
95
95
1
Hi and welcome to Stack Overflow, please take a time to go through the welcome tour to know your way around here (and also to earn your first badge), read how to create a Minimal, Complete, and Verifiable example and also check How to Ask Good Questions so you increase your chances to get feedback and useful answers.
– jess
Jan 2 at 14:35
add a comment |
1
Hi and welcome to Stack Overflow, please take a time to go through the welcome tour to know your way around here (and also to earn your first badge), read how to create a Minimal, Complete, and Verifiable example and also check How to Ask Good Questions so you increase your chances to get feedback and useful answers.
– jess
Jan 2 at 14:35
1
1
Hi and welcome to Stack Overflow, please take a time to go through the welcome tour to know your way around here (and also to earn your first badge), read how to create a Minimal, Complete, and Verifiable example and also check How to Ask Good Questions so you increase your chances to get feedback and useful answers.
– jess
Jan 2 at 14:35
Hi and welcome to Stack Overflow, please take a time to go through the welcome tour to know your way around here (and also to earn your first badge), read how to create a Minimal, Complete, and Verifiable example and also check How to Ask Good Questions so you increase your chances to get feedback and useful answers.
– jess
Jan 2 at 14:35
add a comment |
1 Answer
1
active
oldest
votes
$counts{$user}{$program}++; increments the value stored at key $program in a nested hash which is stored (by reference) as the value of $counts{$user}.
When perl sees the expression $counts{$user}{$program} it will create the (nested) hash stored in $counts{$user} if it does not exist yet. This is called 'autovivification'. perl will also create a key $programin this (nested) hash if it does not exist yet and set its value to undef.
If the value at $counts{$user}{$program} is not yet defined when you call ++ on it, perl will assume, you want a number in this slot and initialize it with 0.
answered Jan 2 at 15:14
clampclamp
36116
add a comment |
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1 Answer
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1 Answer
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active
oldest
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oldest
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active
oldest
votes
$counts{$user}{$program}++; increments the value stored at key $program in a nested hash which is stored (by reference) as the value of $counts{$user}.
When perl sees the expression $counts{$user}{$program} it will create the (nested) hash stored in $counts{$user} if it does not exist yet. This is called 'autovivification'. perl will also create a key $programin this (nested) hash if it does not exist yet and set its value to undef.
If the value at $counts{$user}{$program} is not yet defined when you call ++ on it, perl will assume, you want a number in this slot and initialize it with 0.
answered Jan 2 at 15:14
clampclamp
36116
add a comment |
$counts{$user}{$program}++; increments the value stored at key $program in a nested hash which is stored (by reference) as the value of $counts{$user}.
When perl sees the expression $counts{$user}{$program} it will create the (nested) hash stored in $counts{$user} if it does not exist yet. This is called 'autovivification'. perl will also create a key $programin this (nested) hash if it does not exist yet and set its value to undef.
If the value at $counts{$user}{$program} is not yet defined when you call ++ on it, perl will assume, you want a number in this slot and initialize it with 0.
answered Jan 2 at 15:14
clampclamp
36116
add a comment |
$counts{$user}{$program}++; increments the value stored at key $program in a nested hash which is stored (by reference) as the value of $counts{$user}.
When perl sees the expression $counts{$user}{$program} it will create the (nested) hash stored in $counts{$user} if it does not exist yet. This is called 'autovivification'. perl will also create a key $programin this (nested) hash if it does not exist yet and set its value to undef.
If the value at $counts{$user}{$program} is not yet defined when you call ++ on it, perl will assume, you want a number in this slot and initialize it with 0.
answered Jan 2 at 15:14
clampclamp
36116
$counts{$user}{$program}++; increments the value stored at key $program in a nested hash which is stored (by reference) as the value of $counts{$user}.
When perl sees the expression $counts{$user}{$program} it will create the (nested) hash stored in $counts{$user} if it does not exist yet. This is called 'autovivification'. perl will also create a key $programin this (nested) hash if it does not exist yet and set its value to undef.
If the value at $counts{$user}{$program} is not yet defined when you call ++ on it, perl will assume, you want a number in this slot and initialize it with 0.
answered Jan 2 at 15:14
clampclamp
36116
answered Jan 2 at 15:14
clampclamp
36116
answered Jan 2 at 15:14
clampclamp
36116
answered Jan 2 at 15:14
clampclamp
36116
36116
add a comment |
add a comment |
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Hi and welcome to Stack Overflow, please take a time to go through the welcome tour to know your way around here (and also to earn your first badge), read how to create a Minimal, Complete, and Verifiable example and also check How to Ask Good Questions so you increase your chances to get feedback and useful answers.
– jess
Jan 2 at 14:35