Maintain order within a hash of hashes, and output as .csv - perl

Question

Here's my code:
my %hash = (
'2564' => {
'st_responsible' => 'mname1',
'critical' => '',
'last_modified_by' => 'teamname1',
'transstatus' => '',
'rt_res' => 'pname1'
},
'2487' => {
'st_responsible' => 'mname2',
'critical' => '',
'last_modified_by' => 'teamname2',
'transstatus' => '',
'rt_res' => ''
}
);
print "xnum,st_responsible,critical,last_modified_by,transstatus,rt_res\n";
foreach my $x_number (sort keys %hash)
{
print "$x_number";
foreach my $element (keys %{$hash{$x_number}})
{
print ",$hash{$x_number}{$element}";
}
print "\n";
}
Expected output
xnum,st_responsible,critical,last_modified_by,transstatus,rt_res
2487,mname2,,teamname2,,
2564,mname1,,teamname1,,pname1
Actual output
xnum,st_responsible,critical,last_modified_by,transstatus,rt_res
2487,mname2,,,teamname2,
2564,mname1,,,teamname1,pname1
Please help in letting me know as to how exactly do I preserve the order of this data structure, and then write this to a CSV file.

Answer 1

I would suggest that for this, you'd be better off doing this with a slice, which is a way of extracting a list of values from a hash in a particular order?
#configure field order
my #order = qw ( st_responsible critical last_modified_by transstatus rt_res );
#print header row
print join (",", "xnum", #order ),"\n";
#iterate the rows
foreach my $key ( sort keys %hash ) {
#extract hash slice and join it with commas
print join ( ",", $key, #{$hash{$key}}{#order} ),"\n";
}
This gives:
xnum,st_responsible,critical,last_modified_by,transstatus,rt_res
2487,mname2,,teamname2,,
2564,mname1,,teamname1,,pname1
You can consider Text::CSV - but I'd suggest in this scenario it's overkill, best used when you've got quotes and quoted field separators to worry about. (And you don't).
If you have to deal with not just empty keys, but missing ones, you can make use of map:
my #order = qw ( st_responsible critical last_modified_by
transstatus missing rt_res extra_field_here );
print join (",", "xnum", #order ),"\n";
foreach my $key ( sort keys %hash ) {
print join ( ",", $key, map { $_ // '' } #{$hash{$key}}{#order} ),"\n";
}
(Otherwise you'll get a warning about an undef value).

Answer 2

Perl doesn't guarantee the order of items in the hash, this is the root cause of the issue. Even two different hashes with the same keys can have different order of keys. It may also differ from platform to platform and architecture and perl version.
You need to define another array with the list of keys which you want to print in correct order.
my #keys = qw(st_responsible critical last_modified_by transstatus rt_res);
foreach my $element (#keys) {
... print the value
}
EDIT: As you're trying to write CSV file, consider using Text::CSV which takes care about special characters, correct formatting and things like that.

Answer 3

There's probably a slicker way of achieving this, but give this a go:
use warnings;
use strict;
open my $csv_out, '>', 'out.csv' or die $!;
my #keys = qw(2487 2564);
my #vals = qw(st_responsible critical last_modified_by transstatus rt_res);
print $csv_out "xnum,st_responsible,critical,last_modified_by,transstatus,rt_res\n";
for my $key (#keys){
print $csv_out "$key,";
for my $vals (#vals){
$vals eq $vals[-1] ? print $csv_out "$hash{$key}{$vals}\n" : print $csv_out "$hash{$key}{$vals},";
}
}
This will print out comma-separated values to a csv file out.csv maintaining your original order (by iterating over arrays). If it's the last value it will print a newline.
--- OUTPUT ---
xnum,st_responsible,critical,last_modified_by,transstatus,rt_res
2487,mname2,,teamname2,,
2564,mname1,,teamname1,,pname1