New in Rails: Enumerable#group_by and Array#in_groups_of
Posted by marcel March 01, 2006 @ 08:35 PM
Changeset 3726 adds two little methods to ActiveSupport: Enumerable#group_by and Array#in_groups_of.
Enumerable#group_by is for collecting an enumerable into sets, grouped by the result of a block. Useful, for example, for grouping records by date.
latest_transcripts.group_by(&:day).each do |day, transcripts|
p "#{day} -> #{transcripts.map(&:class) * ', '}"
end
"2006-03-01 -> Transcript"
"2006-02-28 -> Transcript"
"2006-02-27 -> Transcript, Transcript"
"2006-02-26 -> Transcript, Transcript"
Enumerable#group_by will be baked right into Ruby in the future, and currently lives in the 1.9 branch.
Array#in_groups_of let’s you iterate over an array in groups of a certain size, optionally padding any remaining
slots with a specified value (nil by default).
%w(1 2 3 4 5 6 7).in_groups_of(3) {|g| p g}
["1", "2", "3"]
["4", "5", "6"]
["7", nil, nil]
You gotta love the elegant encapsulation afforded by blocks! Yield.
Thank you, a custom ‘group_by’ function seems to end up in every application I write.
However isn’t ‘in_groups_of’ essentialy the same as ‘each_slice’ in the enumerator standard library? (minus the nil padding)
If you take a look at the source, you’ll see that it wraps Enumerator#each_slice, adding padding if necessary. So, yes, it is each_slice plus padding.
cool, i was just about to write something like this ;)
very nice, indeed. this is definitely something you use in almost every app.
It’s a multimap; cool.
Some of the syntax is confusing me – what does the
&:dayargument inlatest_transcripts.group_by(&:day)do? And the same for the
&:classargument inside the block?FYI,
This post broke the entire weblog page in IE. Yeah yeah I know IE sucks but it should still be fixed.
Yeah, I’m confused by the syntax as well.
In:
I think the unfamiliar syntax means, “Call the method ‘day’ on each transcript.” The old-school way would look sort of like this:
More in Scott Raymond’s post.
very nice
very nice