Perl: Generating Arrays inside a Complex Hash

Question

In the quest to make my data more accessible, I want to store my tabulated data in a complex hash. I am trying to grow a 'HoHoHoA' as the script loops over my data. As per the guidelines in 'perldsc':

push @ { $hash{$column[$i]}{$date}{$hour} }, $data[$i];

The script compiles and runs without a problem, but doesn't not add any data to the hash:

print $hash{"Frequency Min"}{"09/07/08"}{"15"}; 

returns nothing even though the keys should exist. Running an 'exists' on the hash shows that it does not exist.

The data file that I am reading looks like this:

DATE       TIME     COLUMN1 COLUMN2 COLUMN3...    
09/06/2008 06:12:56 56.23   54.23   56.35...
09/06/2008 06:42:56 56.73   55.28   54.52...
09/06/2008 07:12:56 57.31   56.79   56.41...
09/06/2008 07:42:56 58.24   57.30   58.86...
.
.
.

I want to group together the values of each column in an array for any given date and hour, hence the three hashes for {COLUMN}, {DATE} and {HOUR}.

The resultant structure will look like this:

%monthData = (
               "COLUMN1" => {
                                    "09/06/2008" => {
                                                      "06" => [56.23,56.73...],
                                                      "07" => [57.31,58.24...]
                                                    }
                            },
               "COLUMN2" => {
                                    "09/06/2008" => {
                                                      "06" => [54.23,55.28...],
                                                      "07" => [56.79,57.30...]
                                                    }
                            },
               "COLUMN3" => {
                                    "09/06/2008" => {
                                                      "06" => [56.35,54.52...],
                                                      "07" => [56.41,58.86...]
                                                    }
                            }
             );

Take a look at my code:

use feature 'switch';
open DATAFILE, "<", $fileName or die "Unable to open $fileName !\n";

    my %monthData;

    while ( my $line = <DATAFILE> ) {

        chomp $line;

        SCANROWS: given ($row) {

            when (0) { # PROCESS HEADERS

                @headers = split /\t\t|\t/, $line;
            }

            default {

                @current = split /\t\t|\t/, $line;
                my $date =  $current[0];
                my ($hour,$min,$sec) = split /:/, $current[1];

                # TIMESTAMP FORMAT: dd/mm/yyyy\t\thh:mm:ss

                SCANLINE: for my $i (2 .. $#headers) {

                    push @{ $monthData{$headers[$i]}{$date}{$hour} }, $current[$i];

                }
            }
        }
    }

    close DATAFILE;

    foreach (@{ $monthData{"Active Power N Avg"}{"09/07/08"}{"06"} }) {
        $sum += $_;
        $count++;
    }

    $avg = $sum/$count; # $sum and $count are not initialized to begin with.
    print $avg; # hence $avg is also not defined.

Hope my need is clear enough. How can I append values to an array inside these sub-hashes?

Answer 1

This should do it for you.

#!/usr/bin/perl

use strict;
use warnings;

use List::Util qw/sum/;
sub avg { sum(@_) / @_ }

my $fileName = shift;

open my $fh, "<", $fileName
    or die "Unable to open $fileName: $!\n";

my %monthData;

chomp(my @headers = split /\t+/, <$fh>);

while (<$fh>) {
    chomp;
    my %rec;
    @rec{@headers} = split /\t+/;
    my ($hour) = split /:/, $rec{TIME}, 2;

    for my $key (grep { not /^(DATE|TIME)$/ } keys %rec) {
     push @{ $monthData{$key}{$rec{DATE}}{$hour} }, $rec{$key};
    }
}

for my $column (keys %monthData) {
    for my $date (keys %{ $monthData{$column} }) {
     for my $hour (keys %{ $monthData{$column}{$date} }) {
      my $avg = avg @{ $monthData{$column}{$date}{$hour} };
      print "average of $column for $date $hour is $avg\n";
     }
    }
}

Things to pay attention to:

• strict and warnings pragmas
• List::Util module to get the sum function
• putting an array in scalar context to get the number of items in the array (in the avg function)
• the safer three argument version of open
• the lexical filehandle (rather than the old bareword style filehandle)
• reading the headers first outside the loop to avoid having to have special logic inside it
• using a hash slice to get the file data into a structured record
• avoiding splitting the time more than necessary with the third argument to split
• avoiding useless variables by only specifying the variable we want to catch in the list assignment
• using grep to prevent the DATE and TIME keys from being put in %monthData
• the nested for loops each dealing with a level in the hash

Answer 2

I hope the following program populates the data structure you want:

#!/usr/bin/perl                        

use strict;
use warnings;
use Data::Dumper;

open my $fh, '<', 'input' or die $!;

my @headers;
for ( split /\t/, ~~ <$fh> ) {
    chomp;
    push @headers, $_ unless /^\t?$/;
}

my %monthData;
while (<$fh>) {
    my @line;
    for ( split /\t/ ) {
        chomp;
        push @line, $_ unless /^\t?$/;
    }

    for my $i ( 2 .. $#headers ) {
        my ($hour) = split /:/, $line[1];
        push @{ $monthData{ $headers[$i] }->{ $line[0] }->{$hour} }, $line[$i];
    }
}

print Dumper \%monthData;

Answer 3

Here's how I would write a program to do that.

#! /usr/bin/env perl
use strict;
use warnings;
use 5.010; # for say and m'(?<name>)'

use YAML;
use Data::Dump 'dump';

my(%data,%original);
while( my $line = <> ){
  next unless $line =~ m'
    ^ \s*
      (?<day>   0?[1-9] | [12][0-9] | 3[0-1] ) /
      (?<month> 0?[1-9] | 1[0-2] ) /
      (?<year>  [0-9]{4} )
      \s+
      (?<hour>   0?[1-9] | 1[0-9] | 2[0-4] ) :
      (?<minute> 0?[1-9] | [1-5][0-9] ) :
      (?<second> 0?[1-9] | [1-5][0-9] )
      \s+
      (?<columns> .* )
  'x;
  my @columns = split ' ', $+{columns};

  push @{
    $data{ $+{year}  }
         { $+{month} }
         { $+{day}   }
         { $+{hour}  }
  }, \@columns; # or [@columns]

  # If you insist on having it in that data structure you can do this:
  my $count = 1;
  my $date = "$+{day}/$+{month}/$+{year}";
  for my $column ( @columns ){
    my $col = 'COLUMN'.$count++;
    push @{ $original{$col}{$date}{$+{hour}} }, $column;
  }
}

say Dump \%data, \%original; # YAML
say dump \%data, \%original; # Data::Dump

Given this input

DATE       TIME     COLUMN1 COLUMN2 COLUMN3
09/06/2008 06:12:56 56.23   54.23   56.35
09/06/2008 06:42:56 56.73   55.28   54.52
09/06/2008 07:12:56 57.31   56.79   56.41
09/06/2008 07:42:56 58.24   57.30   58.86

Either "perl program.pl datafile" or "perl program.pl < datafile"

YAML

---
2008:
  06:
    09:
      06:
        -
          - 56.23
          - 54.23
          - 56.35
        -
          - 56.73
          - 55.28
          - 54.52
      07:
        -
          - 57.31
          - 56.79
          - 56.41
        -
          - 58.24
          - 57.30
          - 58.86
---
COLUMN1:
  09/06/2008:
    06:
      - 56.23
      - 56.73
    07:
      - 57.31
      - 58.24
COLUMN2:
  09/06/2008:
    06:
      - 54.23
      - 55.28
    07:
      - 56.79
      - 57.30
COLUMN3:
  09/06/2008:
    06:
      - 56.35
      - 54.52
    07:
      - 56.41
      - 58.86

Data::Dump

(
  {
    2008 => {
          "06" => {
                "09" => {
                      "06" => [["56.23", "54.23", "56.35"], ["56.73", "55.28", "54.52"]],
                      "07" => [["57.31", "56.79", "56.41"], ["58.24", "57.30", "58.86"]],
                    },
              },
        },
  },
  {
    COLUMN1 => {
                 "09/06/2008" => { "06" => ["56.23", "56.73"], "07" => ["57.31", "58.24"] },
               },
    COLUMN2 => {
                 "09/06/2008" => { "06" => ["54.23", "55.28"], "07" => ["56.79", "57.30"] },
               },
    COLUMN3 => {
                 "09/06/2008" => { "06" => ["56.35", "54.52"], "07" => ["56.41", "58.86"] },
               },
  },
)