NAME

List::GroupBy - Group a list of hashref's to a multilevel hash of hashrefs of arrayrefs

SYNOPSIS

use List::GroupBy qw( groupBy );

my @list = (
    { firstname => 'Fred',   surname => 'Blogs', age => 20 },
    { firstname => 'George', surname => 'Blogs', age => 30 },
    { firstname => 'Fred',   surname => 'Blogs', age => 65 },
    { firstname => 'George', surname => 'Smith', age => 32 },
    { age => 99 },
);

my %groupedList = groupBy ( [ 'surname', 'firstname' ], @list );

# %groupedList => (
#     'Blogs' => {
#         'Fred' => [
#             { firstname => 'Fred',   surname => 'Blogs', age => 20 },
#             { firstname => 'Fred',   surname => 'Blogs', age => 65 },
#         ],
#         'George' => [
#             { firstname => 'George', surname => 'Blogs', age => 30 },
#         ],
#     },
#     'Smith' => {
#         'George' => [
#             { firstname => 'George', surname => 'Smith', age => 32 },
#         ],
#     },
#     '' => {
#         '' => [
#             { age => 99 },
#         },
#     },
# )


%groupedList = groupBy(
    {
        keys => [ 'surname', 'firstname' ],
        defaults => { surname => 'Blogs' }
    },
    @list
);

# %groupedList => (
#     Blogs => {
#         Fred => [
#             { firstname => 'Fred',   surname => 'Blogs', age => 20 },
#             { firstname => 'Fred',   surname => 'Blogs', age => 65 },
#         ],
#         George => [
#             { firstname => 'George', surname => 'Blogs', age => 30 },
#         ],
#         '' => [
#             { age => 99 },
#         ],
#     },
#     Smith => {
#         George => [
#             { firstname => 'George', surname => 'Smith', age => 32 },
#         ],
#     },
# )


%groupedList = groupBy (
    {
        keys => [ 'surname', 'firstname' ],
        defaults => { surname => 'Blogs' },
        operations => { surname => sub { uc $_[0] } },
    },
    @list
);

# %groupedList => (
#     BLOGS => {
#         Fred => [
#             { firstname => 'Fred',   surname => 'Blogs', age => 20 },
#             { firstname => 'Fred',   surname => 'Blogs', age => 65 },
#         ],
#         George => [
#             { firstname => 'George', surname => 'Blogs', age => 30 },
#         ],
#         '' => [
#             { age => 99 },
#         ],
#     },
#     SMITH => {
#         George => [
#             { firstname => 'George', surname => 'Smith', age => 32 },
#         ],
#     },
# )

DESCRIPTION

List::GroupBy provides functions to group a list of hashrefs in to a hash of hashrefs of arrayrefs.

FUNCTIONS

• groupBy( [ 'primary key', 'secondary key', ... ], LIST )

  If called with and array ref as the first parameter then groupBy will group the list by the keys provided in the array ref.

  Note: undefined values for a key will be defaulted to the empty string.

  Returns:

  • List Context - a hash of hashrefs of arrayrefs
  • Scalar Context - a hashref of hashrefs of arrayrefs

• groupBy( { keys => [ 'key', ... ], defaults => { 'key' => 'default', ... }, operations => { 'key' => sub, ... }, LIST )

  More advanced options are available by calling groupBy with a hash ref of options as the first parameter. Available options are:

  • keys (Required)

    An array ref of the keys to use for grouping. The order of the keys dictates the order of the grouping. So the first key is the primary grouping, the second key is used for the secondary grouping under the primary grouping an so on.

  • defaults (Optional)

    A hash ref of defaults to use one or more keys. If a key for an item is undefined and there's an entry in the defaults option then that will be used. If no default value has been supplied for a key then the empty string will be used.

  • operations (Optional)

    A hash ref mapping keys to a function to use to normalise value's when grouping. If there's no entry for a key then the value is just used as is.

    Each funtion is passed the value as it's only parameter and it's return value is used for the key.

    If you wish to make a grouping case-insensitive then you can use an operation on that key that simply folds (fc())the case e.g.

      %groupedList = groupBy (
          {
              keys => [ 'surname', 'firstname' ],
              defaults => { surname => 'Blogs' },
              operations => {
                  surname => sub { fc( $_[0] ) },
                  firstname => sub { fc ( $_[0] ) },
              },
          },
          @list
      );
    

  Returns:

  • List Context - a hash of hashrefs of arrayrefs
  • Scalar Context - a hashref of hashrefs of arrayrefs

LICENSE

Copyright (C) Jason Cooper.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

AUTHOR

Jason Cooper JLCOOPER@cpan.org