NAME
Hash::Subset - Produce subset of a hash
VERSION
This document describes version 0.007 of Hash::Subset (from Perl
distribution Hash-Subset), released on 2022-07-27.
SYNOPSIS
use Hash::Subset qw(
hash_subset
hashref_subset
hash_subset_without
hashref_subset_without
merge_hash_subset
merge_overwrite_hash_subset
merge_ignore_hash_subset
merge_hash_subset_without
merge_overwrite_hash_subset_without
merge_ignore_hash_subset_without
);
# using keys specified in an array
my %subset = hash_subset ({a=>1, b=>2, c=>3}, ['b','c','d']); # => (b=>2, c=>3)
my $subset = hashref_subset({a=>1, b=>2, c=>3}, ['b','c','d']); # => {b=>2, c=>3}
# using keys specified in another hash
my %subset = hash_subset ({a=>1, b=>2, c=>3}, {b=>20, c=>30, d=>40}); # => (b=>2, c=>3)
my $subset = hashref_subset({a=>1, b=>2, c=>3}, {b=>20, c=>30, d=>40}); # => {b=>2, c=>3}
# filtering keys using a coderef
my %subset = hash_subset ({a=>1, b=>2, c=>3}, sub {$_[0] =~ /[bc]/}); # => (b=>2, c=>3)
my $subset = hashref_subset({a=>1, b=>2, c=>3}, sub {$_[0] =~ /[bc]/}); # => {b=>2, c=>3}
# multiple filters: array, hash, coderef
my %subset = hash_subset ({a=>1, b=>2, c=>3, d=>4}, {c=>1}, [qw/b/], sub {$_[0] =~ /[bcd]/}); # => (b=>2, c=>3, d=>4)
my $subset = hashref_subset({a=>1, b=>2, c=>3, d=>4}, {c=>1}, [qw/b/], sub {$_[0] =~ /[bcd]/}); # => {b=>2, c=>3, d=>4}
# excluding keys
my %subset = hash_subset_without ({a=>1, b=>2, c=>3}, ['b','c','d']); # => (a=>1)
my $subset = hashref_subset_without({a=>1, b=>2, c=>3}, ['b','c','d']); # => {a=>1}
A use case is when you use hash arguments:
sub func1 {
my %args = @_; # known arguments: foo, bar, baz
...
}
sub func2 {
my %args = @_; # known arguments: all func1 arguments as well as qux, quux
# call func1 with all arguments passed to us
my $res = func1(hash_subset(\%args, [qw/foo bar baz/]));
# postprocess result
...
}
If you use Rinci metadata in your code, this will come in handy, for
example:
my %common_args = (
foo => {...},
bar => {...},
baz => {...},
);
$SPEC{func1} = {
v => 1.1,
args => {
%common_args,
},
};
sub func1 {
my %args = @_;
...
}
$SPEC{func2} = {
v => 1.1,
args => {
%common_args,
# func2 supports all func1 arguments plus a couple of others
qux => { ... },
quux => { ... },
},
};
sub func2 {
my %args = @_;
# call func1 with all arguments passed to us
my $res = func1(hash_subset(\%args, $SPEC{func1}{args}));
# postprocess result
...
}
Merging subset to another hash:
my %target = (a=>1, b=>2);
merge_hash_subset(\%target, {foo=>1, bar=>2, baz=>3}, qr/ba/); # %target becomes (a=>1, b=>2, bar=>2, baz=>3)
merge_hash_subset_without(\%target, {foo=>1, bar=>2, baz=>3}, qr/ba/); # %target becomes (a=>1, b=>2, foo=>1)
DESCRIPTION
Keywords: hash arguments, hash picking, hash grep, hash filtering, hash
merging
FUNCTIONS
None exported by default.
hash_subset
Usage:
my %subset = hash_subset (\%hash, @keys_srcs);
my $subset = hashref_subset(\%hash, @keys_srcs);
Where each @keys_src element can either be an arrayref, a hashref, a
Regexp object, or a coderef. Coderef will be called with args($key,
$value) and return true when key should be included.
Produce subset of %hash, returning the subset hash (or hashref, in the
case of "hashref_subset" function).
Perl lets you produce a hash subset using the hash slice notation:
my %subset = %hash{"b","c","d"};
The difference with "hash_subset" is: 1) hash slice is only available
since perl 5.20 (in previous versions, only array slice is available);
2) when the key does not exist in the array, perl will create it for you
with "undef" as the value:
my %hash = (a=>1, b=>2, c=>3);
my %subset = %hash{"b","c","d"}; # => (b=>2, c=>3, d=>undef)
So basically "hash_subset" is equivalent to:
my %subset = %hash{grep {exists $hash{$_}} "b","c","d"}; # => (b=>2, c=>3)
and available for perl earlier than 5.20. In addition to that,
hash_subset() accepts arrayref & Regexp object as well as
hashref/coderef, and several of them.
hashref_subset
See "hash_subset".
hash_subset_without
Like "hash_subset", but reverses the logic: will create subset that only
includes keys not in the specified arrays/hashes/Regexps/coderefs.
hashref_subset_without
See "hash_subset_without".
merge_hash_subset
Usage:
merge_hash_subset (\%h1, \%h2, @keys_src);
merge_overwrite_hash_subset(\%h1, \%h2, @keys_src);
merge_ignore_hash_subset (\%h1, \%h2, @keys_src);
"merge_hash_subset" selects a subset of hash %h2 (using @keys_src, just
like in "hash_subset") and merge the subset to hash %h1. This is
basically a convenience shortcut for:
my %subset = hash_subset(\%h2, @keys_src);
for my $key (keys %subset) {
die "Duplicate key when merging subset: $key" if exists $h1{$key];
$h1{$key} = $subset{$key};
}
while "merge_overwrite_hash_subset" does something like this:
my %subset = hash_subset(\%h2, @keys_src);
for my $key (keys %subset) {
$h1{$key} = $subset{$key};
}
and "merge_ignore_hash_subset" does something like this:
my %subset = hash_subset(\%h2, @keys_src);
for my $key (keys %subset) {
next if exists $h1{$key};
$h1{$key} = $subset{$key};
}
merge_overwrite_hash_subset
See "merge_hash_subset".
merge_ignore_hash_subset
See "merge_hash_subset".
merge_hash_subset_without
Usage:
merge_hash_subset_without (\%h1, \%h2, @keys_src);
merge_overwrite_hash_subset_without(\%h1, \%h2, @keys_src);
merge_ignore_hash_subset_without (\%h1, \%h2, @keys_src);
These are like "merge_hash_subset", "merge_overwrite_hash_subset", and
"merge_ignore_hash_subset" except these routines will merge subset from
%h2 that do *not* contain keys specified by @keys_src.
merge_overwrite_hash_subset_without
See "merge_hash_subset_without".
merge_ignore_hash_subset_without
See "merge_hash_subset_without".
HOMEPAGE
Please visit the project's homepage at
.
SOURCE
Source repository is at .
SEE ALSO
Hash::MoreUtils provides various ways to create hash subset ("slice")
through its "slice_*" functions. It does not provide way to specify
subset keys via the keys of %another_hash, but that can be done
trivially using "keys %another_hash". Hash::Subset is currently more
lightweight than Hash::MoreUtils.
Tie::Subset::Hash to create a tied version of a hash subset (a "view" of
a subset of a hash).
Hash::Util::Pick also allows you to create a hash subset by specifying
the wanted keys in a list or via filtering using a coderef. This XS
module should perhaps be preferred over Hash::Subset for its
performance, but there are some cases where you cannot use XS modules.
See some benchmarks in Bencher::Scenarios::HashPicking.
AUTHOR
perlancar
CONTRIBUTING
To contribute, you can send patches by email/via RT, or send pull
requests on GitHub.
Most of the time, you don't need to build the distribution yourself. You
can simply modify the code, then test via:
% prove -l
If you want to build the distribution (e.g. to try to install it locally
on your system), you can install Dist::Zilla,
Dist::Zilla::PluginBundle::Author::PERLANCAR, and sometimes one or two
other Dist::Zilla plugin and/or Pod::Weaver::Plugin. Any additional
steps required beyond that are considered a bug and can be reported to
me.
COPYRIGHT AND LICENSE
This software is copyright (c) 2022, 2020, 2019 by perlancar
.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
BUGS
Please report any bugs or feature requests on the bugtracker website
When submitting a bug or request, please include a test-file or a patch
to an existing test-file that illustrates the bug or desired feature.