I have array that looks like
[nil, nil, nil, nil, 5, 6, 7, 8, 9, 10, 11, nil, nil, nil, nil, nil, 17, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, 50, 51]
I want to "unflatten" it, so it'd look like
[[5,6,7,8,9,10,11],[17], [50,51]]
What would be the easiest way to achieve that?
arr.slice_before(&:nil?).map(&:compact).reject(&:empty?)
Just out of curiosity, O(N):
arr.inject([[]]) do |memo, e|
e ? memo.last << e : (memo << [] unless memo.last.empty?)
memo
end
Or, with modern ruby goodness:
arr.each_with_object([[]]) do |e, memo|
e && memo.last << e || (memo << [] unless memo.last.empty?)
end
And, totally out of curiosity (it’s a joke, please, do not use):
JSON.parse arr.to_json
.gsub(/\D{2,}/, '],[')
.gsub(/\A\D+/, '[[')
.gsub(/\D+\z/, ']]')
nil or integers, we could write arr.join(' ').strip.split(/\s{2,}/).map { |s| s.split(/\s/).map(&:to_i) }.I thought about
a.slice_when { |e1, e2| e1 != e2 && e2.nil? }.map(&:compact)
# => [[5, 6, 7, 8, 9, 10, 11], [17], [50, 51]]
Enumerable#chunk_while, which I proposed, coming in Ruby 2.3: bugs.ruby-lang.org/issues/10769.chunk_by, so I can see the procedure?We can use Enumerable#chunk for this:
arr = [nil, nil, nil, nil, 5, 6, 7, 8, 9, 10, 11, nil, nil, nil, nil, nil, 17,
nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, 50, 51]
arr.chunk(&:nil?).reject(&:first).map(&:last)
#=> [[5, 6, 7, 8, 9, 10, 11], [17], [50, 51]]
The steps:
enum = arr.chunk(&:nil?)
#=> #<Enumerator: #<Enumerator::Generator:0x007fd303042440>:each>
We can examine the elements of the enumerator enum by converting it to an array:
enum.to_a
#=> [[true, [nil, nil, nil, nil]],
# [false, [5, 6, 7, 8, 9, 10, 11]],
# [true, [nil, nil, nil, nil, nil]],
# [false, [17]],
# [true, [nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil]],
# [false, [50, 51]]]
Two more steps:
a = enum.reject(&:first)
#=> [[false, [5, 6, 7, 8, 9, 10, 11]],
# [false, [17]],
# [false, [50, 51]]]
a.map(&:last)
#=> [[5, 6, 7, 8, 9, 10, 11], [17], [50, 51]]
Edit: Thanks to @Stefan, today I learned something new about the way chunk handles nils. As he suggests, we can simplify this to:
arr.chunk { |e| e && false }.map(&:last)
#=> [[5, 6, 7, 8, 9, 10, 11], [17], [50, 51]]
Well, maybe that's not exactly what he said, but it works just as well. (My variant is more of a head-scratcher.)
a.chunk { |e| e && true }.map(&:last)