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!

Replies are listed 'Best First'.
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]
      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]
        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: 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]
      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]
        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]

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