use List::Util module
To create a collection of objects (e.g. hashes)
my @collection = ({%hash1},{%hash2})
For a hash,
$hash{key} and %hash->{key} are equivalent
Use foreach to modify content of a list
Use grep to filter a list
Use of map
Use map to transform one list to another
my ($from) = map /^From:\s+(.*)$/, @message_lines;
my @text_files = map { /(.*)\.txt$/ } @files;
Use map to transform elements of a data structure into a new structure
Use map and grep together for complex operations
Operation applied by map should not modify element
Removing duplicates from an array
my %seen = ();
my @unique = grep { ! $seen{ $_ }++ } @a;
Sorting a collection
Minimize call to function
Instead of using
my @sorted = sort { -M $a <=> -M $b } @files;
use
my @sorted =
sort { ( $m{$a} ||= -M $a ) <=> ( $m{$b} ||= -M $b ) }
@files;
where $m{$a} ||= -M $a keeps the cached value of -M in $m{$a}
Schwartzian Transform:
my @sorted_names =
map { $_->[0] } # 4. extract original names
sort { $a->[1]
<=>
$b->[1] } # 3. sort [name, key] tuples
map { [ $_, -M ] } # 2. create [name, key] tuples
@files; # 1. the input data
References
Take reference of array and change content
$ref = \@ary;
@$ref[1] = "new val";
These two are the same
$list_ref->[1];
@$list_ref[1];
Autovivification creates reference on the fly
$ary->[3] = 'NEW ELEMENT'
A Hash collection of array references
my %hash = (hash1=>[qw(item1 item2)],
hash2=>[qw(item3 item4)],
hash3=>[('item5')]);
hash2=>[qw(item3 item4)],
hash3=>[('item5')]);
foreach my $style (keys (%hash)) {
say $style;
my @filelist = @{$hash{$style}};
foreach my $ele (@filelist) {
say 'array element = ', $ele;
}
}
say $style;
my @filelist = @{$hash{$style}};
foreach my $ele (@filelist) {
say 'array element = ', $ele;
}
}
A array collection of hash references
my %h1 = (id => 'A123', action => 'AMEND');
my %h2 = (id => 'A456', action => 'NEW');
my %h2 = (id => 'A456', action => 'NEW');
my @a = ({%h1}, {%h2});
for (@a) {
my %h = %$_;
say $h{id};
say $h{action};
}
my %h = %$_;
say $h{id};
say $h{action};
}
}
