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.