New named parameters to .classify

[FCO]

Id like to suggest to add:

• :&reduce
• :&produce
• :$initial-value

so,

^10.classify: * %% 2, :reduce(&[+])

would return

{True => 25, False => 20}

,

^10.classify: * %% 2, :produce(&[+])

would return

({}, {True => 0}, {True => 0, False => 1}, {True => 2, False => 1}, {True => 2, False => 4}, {True => 6, False => 4}, {True => 6, False => 9}, {True => 12, False => 9}, {True => 12, False => 16}, {True => 20, False => 16}, {True => 20, False => 25}).Seq

and

^5.classify: * %% 2, :produce(-> %agg, $i { %agg{$i} = <a e i o u>[$i]; %agg }), :initial-value{}

would return

{True => {0 => "a", 2 => "I", 4 => "u"}, False => {1 => "e", 3 => "o"}}

That would also be interesting to add the :$initial-value (or with any name) to .reduce and .produce

[AlexDaniel]

And which problem are we trying to solve here exactly?

[FCO]

I had to do that by hand some times, and ended up not using classify because it would be worst to write and have to loop throw each key and reduce each value (on reduce case)... making the classify do that, you can reduce/produce iterating only once...

[Altai-man]

Why not just:

> (^10).classify(* %% 2).map({ .key => [+] .value })
(False => 25 True => 20)

for the first one? Because it adds some symmetry with produce?

[FCO]

It iterates twice each element...

and what about multi level classify?

[AlexDaniel]

Do we have some examples of this functionality being used/implemented in real code? Maybe in the ecosystem?

[jnthn]

Does this proposal apply to categorize also?

[jnthn]

That would also be interesting to add the :$initial-value (or with any name) to .reduce and .produce

How would this interact with the current semantics of things like [+] () and [+] 1, which use multi-dispatch on the target operator?

Further, how is it better than (flat $initial-value, @values).reduce(&reducer)?

[AlexDaniel]

IRC discussion: https://colabti.org/irclogger/irclogger_log/perl6-dev?date=2019-04-05#l181

[lizmat]

Updated IRC discussion link: https://irclogs.raku.org/perl6-dev/2019-04-05.html#23:03-0003