Array of sorted key/value pairs to sorted array of keys and hash

I am developing a Catalyst app which uses Template::Toolkit as template engine. One page needs a list of equal input elements. They can be taken from an array but I need both sort order and a descriptive label for the element开发者_C百科.

For having a sort order I would use an array. For storing an additional value per key a hash is perfect. How to combine both in TT? I could use both things but that seems ugly and can cause mistakes when changing the fields.

However, I prefer doing this in TT because both the descriptions and the order of form elements is a front-end thing.

This is how I would do it in pure Perl:

#!/usr/bin/perl -w

use 5.10.0;

# definition of description and order in 1 step
my @fields = (
        property_foo => "Some property",
        property_bar => "Important field",
        property_baz => "Something else",
);

# extract information
my %descriptions = @fields;
my @order = @fields[grep {($_ + 1) % 2} 0..(scalar @fields - 1)];

say "=== natural perl sort order ===";
foreach (keys %descriptions) {say $_};

say "=== wanted output ===";
foreach (@order) {
        say $descriptions{$_} . ": [label for $_]";
}

Outputs:

=== natural perl sort order ===
property_baz
property_foo
property_bar
=== wanted output ===
Some property: [label for property_foo]
Important field: [label for property_bar]
Something else: [label for property_baz]

This is what I write in my template:

[%
order = (
    property_foo,
    property_bar,
    property_baz,
);

descriptions = {
    property_foo => "Some property",
    property_bar => "Important field",
    property_baz => "Something else",
}

FOREACH property IN order %]
    [% descriptions.$property %]: <input name="[% property %]" />
[% END %]

However, it is really ugly to have the same information (list of fields) twice. I want to avoid editing the list twice and with a longer list of fields it gets really annoying (about 20 items, not long enough to do some database stuff).

It's amazing how people complicate easy stuff!

You don't need the @fields array. Please read the perldoc about keys, values and sort.

# untested sketch
my %description = ( prop23 => "foo", prop24 => "bar" );
foreach my $key(sort (keys %description)) {
    print $key, " is: ", $description{$key}, "\n";   # or whatever
}

Addendum: Regarding the order of keys, just do the following:

my @arbitraryOrder = qw(prop42 prop35 prop1 ...);  # allows to map number to key
my %keytoNumber = ();                              # will map keys to numbers
foreach my $i(0..$#arbitraryOrder) $keyToNumber{$arbitraryOrder[$i]} = $i;

Writing the comparison function for sort is left as an exercise :)

You might be interested in Tie::IxHash

It is a "hash" that keeps the order in which you add keys (value updates do not affect sorting).

EDIT: A brief example:

use warnings;
use strict;

use Tie::IxHash; 
tie my %H, "Tie::IxHash"; 
$H{foo} = 1; 
$H{bar} = 2; 
# order of keys is now always 'foo', 'bar'

print keys %H;

EDIT2: I've tried it out, and it actually works:

#!/usr/bin/perl -w

use strict;
use Template;
use Tie::IxHash;

# my %h; # this breaks ordering
tie my %H, "Tie::IxHash"; # this keeps ordering
@H{qw/f oo b a r/} = 1..100;
# don't define $H{'keys'} or you'll get disappointed

my $tpl = Template->new();
$tpl->process(\*DATA, {hash=>\%H});

__DATA__
[% FOREACH k IN hash.keys %]
     [% k %] => [% hash.$k %]
[% END %]

If you need ordering and multiple pieces of information then you should consider an array of hash references.

my @fields = (
  { id => 'property_foo',
    label => 'Some property' },
  { id => 'property_bar',
    label => 'Important field' },
  { id => 'property_baz',
    label => 'Something else' },
);

foreach (@fields) {
  print "ID: $_->{id}, Label: $_->{label}\n";
}

If the complexity increases much beyond this, you might consider replacing the hashrefs with real objects.

And, in TT, it looks like this:

[%-
properties = [
  {id => 'property_foo',
   label => 'Some property'},
  {id => 'property_bar',
   label => 'Important field'},
  {id => 'property_baz',
   label => 'Something else'},
];
-%]

[%- FOREACH property IN properties %]
    [% property.label %]: <input name="[% property.id %]" />
[% END %]

Actually if you want your hash alphabetically sorted by key, Template::Toolkit does that for you.

test.pl

use strict;
use warnings;

use Template;

my %hash = qw' a 1 b 2 c 3 ';

my $config = {
  INCLUDE_PATH => '/search/path',
};
my $input = 'test.tt2';

my $template = Template->new( $config );
$template->process( $input, {
  hash => \%hash,
})

test.tt2

[% FOREACH hash -%]
[% key %] => [% value %]
[% END %]

output

a => 1
b => 2
c => 3