Using a Hash Variable in an If Statement

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

Hi Monks, I have a question regarding the use of a hash. The goal of the following script is to loop through a file that looks like this:

 
20131201.06372602.mcp
APRL 7.1963
BEBP 7.1979
CASY 7.3879
DONT 7.3196
DUBY 6.3729
FOOT 7.1496
GRAW 7.0046
KNYN 6.7313
LEON 7.4596
MICH 7.5579
RAPH 7.0563
RKST 6.6879
SAMH 6.9529
SHRD 6.2829
SPLN 6.1113
20131202.02185602.mcp
APRL -2.1870
BEBP -2.3270
CASY -1.0153
DONT -0.1453
DUBY -1.9920
FOOT -2.1903
GRAW -1.5937
KNYN -2.0403
LEON -0.6237
MICH -1.5737
RAPH -1.3287
RKST -2.5337
SAMH -1.9653
SHRD -2.4087
SPLN -2.2053
[download]

Which is repeated >100 times. I am using a hash, because I first want to assign each string (DONT, MICH, etc) a number, which I have done so here in this hash:

my %station_name = (
DONT => "1",
MICH => "2",
LEON => "3",
RAPH => "4",
SPLN => "5",
SHRD => "6",
CASY => "7",
APRL => "8",
FOOT => "9",
BEBP => "10",
RKST => "11",
DUBY => "12",
SAMH => "13",
GRAW => "14",
KNYN => "15",
KP01 => "16",
KP02 => "17",
KP03 => "18",
KP04 => "19",
KP05 => "20",
);
[download]

What I want to do is loop through the above file (which is the format above), and for each station (DONT, MICH, etc), print out the respective number (time). However, I am unsure how to do this in an if-statement. What I have is below:

 for ($i = 0; $i < @rat_event; $i++) {
    chomp($rat_event[$i]);
    ($station, $delaytime) = (split /\s+/, $rat_event[$i])[0,1];
    # create a Hash for the Stations.
    if ($station = %station_name) {
        #I don't know what do do here.
}

close(rat_event);
close(RAT_STA);
[download]

where rat_event is the file I'm looping through, $station and $delaytime are the values from above, but when it comes to the 'if' statement, I'm unsure how to use the hash to output something like:

1
time1
time2
...
time_n
2
time1
time2
...
time_n.
[download]

Any help would be appreciated. Thanks!

Comment on Using a Hash Variable in an If Statement Select or Download Code

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Re: Using a Hash Variable in an If Statement by toolic (Bishop) on May 11, 2015 at 19:32 UTC
use warnings; use strict; my @names = qw( DONT MICH LEON RAPH SPLN SHRD CASY APRL FOOT BEBP RKST DUBY SAMH GRAW KNYN KP01 KP02 KP03 KP04 KP05 ); my %data; while (<DATA>) { next if /mcp/; chomp; my ($s, $n) = split; push @{ $data{$s} }, $n; } my $i = 1; for my $name (@names) { print "$i\n"; print "$_\n" for @{ $data{$name} }; $i++; } __DATA__ 20131201.06372602.mcp APRL 7.1963 BEBP 7.1979 CASY 7.3879 DONT 7.3196 DUBY 6.3729 FOOT 7.1496 GRAW 7.0046 KNYN 6.7313 LEON 7.4596 MICH 7.5579 RAPH 7.0563 RKST 6.6879 SAMH 6.9529 SHRD 6.2829 SPLN 6.1113 20131202.02185602.mcp APRL -2.1870 BEBP -2.3270 CASY -1.0153 DONT -0.1453 DUBY -1.9920 FOOT -2.1903 GRAW -1.5937 KNYN -2.0403 LEON -0.6237 MICH -1.5737 RAPH -1.3287 RKST -2.5337 SAMH -1.9653 SHRD -2.4087 SPLN -2.2053 [download] Prints: `1 7.3196 -0.1453 2 7.5579 -1.5737 3 7.4596 -0.6237 4 7.0563 -1.3287 5 6.1113 -2.2053 6 6.2829 -2.4087 7 7.3879 -1.0153 8 7.1963 -2.1870 9 7.1496 -2.1903 10 7.1979 -2.3270 11 6.6879 -2.5337 12 6.3729 -1.9920 13 6.9529 -1.9653 14 7.0046 -1.5937 15 6.7313 -2.0403 16 17 18 19 20` [download]	[reply] [d/l] [select]
Re^2: Using a Hash Variable in an If Statement by Bama_Perl (Acolyte) on May 11, 2015 at 20:21 UTC
Could you possible explain the first while loop: `my %data; while (<DATA>) { next if /mcp/; chomp; my ($s, $n) = split; push @{ $data{$s} }, $n; }` [download] If my file I'm trying to read in is called rat_event, should I open it above, such as here: `open(rat_event,"RAT_EVENT"); @rat_event = <rat_event>;` [download] and then do: `my %rat_event; while <RAT_EVENT> { # Same as above }` [download] Thanks for the help.	[reply] [d/l] [select]
Re^3: Using a Hash Variable in an If Statement by edimusrex (Monk) on May 11, 2015 at 20:32 UTC
The first part is saying "check each line of the file (assigned to DATA, in your case rat_event) and if the line is equal to mcp, skip it (would skip 20131201.06372602.mcp and 20131202.02185602.mcp). Else chomp the line (remove new line and carriage return) and split the line into 2 variables (s and n, since no character is specified for the split it defaults to a space which would give you the station name and the time) and once it has those variables assigned it puts the values into the hash %data so s => 'n'. Yes you should load the file first as your code is shown `open my $fh, "<rat_event" or die "Failed to open:$!"; while(<$fh>) { #do something }` [download]	[reply] [d/l]
Re^4: Using a Hash Variable in an If Statement by Bama_Perl (Acolyte) on May 11, 2015 at 20:36 UTC
Re: Using a Hash Variable in an If Statement by edimusrex (Monk) on May 11, 2015 at 20:14 UTC
Adding to toolic's code if you wanted the station name plus the run number added to the output you could do the following `#!/usr/bin/perl use warnings; #use strict; my @names = qw( DONT MICH LEON RAPH SPLN SHRD CASY APRL FOOT BEBP RKST DUBY SAMH GRAW KNYN KP01 KP02 KP03 KP04 KP05 ); my %data; open my $file, "<", "rat_event.txt" or die "Can't open file:$!"; while(<$file>) { next if /\.mcp/; chomp; my ($s, $n) = split; push @{ $data{$s} }, $n; } my $i = 1; for my $name (@names) { print "$name\n"; my $x = 1; for (@{$data{$name}}) { print "Time $x : $_\n"; $x++; } print "\n"; $i++; } close($file);` [download]	[reply] [d/l]
Re^2: Using a Hash Variable in an If Statement by Bama_Perl (Acolyte) on May 11, 2015 at 20:51 UTC
I apologize for the many questions, but what does the `print "$_\n" for @{ $data{$name} };` do? Is this just saying that I want to print a new line for each piece of data within each $name? Thanks.	[reply] [d/l]
Re^3: Using a Hash Variable in an If Statement by edimusrex (Monk) on May 11, 2015 at 21:00 UTC
it means print each value for the hash referenced at $data{$name} (which would look like this in a data dump (data{APRL} => 7.1963). $_ is a special variable which references the current element. This is the same thing `foreach my $line (@{$data{$name}}) { #do something }` [download] Where $line is the same thing as $_, more than 1 way to skin a cat. So it's say print out the hash value of the specified key and also print a new line with it so everything won't be bunched up on a single line. Hope that makes sense.	[reply] [d/l]
Re^4: Using a Hash Variable in an If Statement by Bama_Perl (Acolyte) on May 11, 2015 at 22:15 UTC
Re^5: Using a Hash Variable in an If Statement by 2teez (Vicar) on May 12, 2015 at 00:04 UTC
Re^5: Using a Hash Variable in an If Statement by edimusrex (Monk) on May 12, 2015 at 00:45 UTC
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