I'd like to take input such as:
[1,2,4,5,6,7,9,13]
and turn it into something like the following:
[[1,2],[4,7],[9,9],[13,13]]
Each sub-array represents a range of integers.
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2Are you asking if there is code to do this already? Are you asking because you're trying to roll your own and having trouble implementing it?bobbymcr– bobbymcr2011-12-24 00:11:53 +00:00Commented Dec 24, 2011 at 0:11
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I'm rolling my own. Seems there are always interesting ways to implement this kind of thing in Ruby.Larsenal– Larsenal2011-12-24 00:14:23 +00:00Commented Dec 24, 2011 at 0:14
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By which conditions are the ranges supposed to be built?cvshepherd– cvshepherd2011-12-24 00:18:25 +00:00Commented Dec 24, 2011 at 0:18
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A continuous integer sequence in the array should compose a "range" which is really just an array with the start and end.Larsenal– Larsenal2011-12-24 00:19:09 +00:00Commented Dec 24, 2011 at 0:19
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1possible duplicate of Array of indexes to array of rangesAndrew Grimm– Andrew Grimm2011-12-24 05:16:42 +00:00Commented Dec 24, 2011 at 5:16
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5 Answers
Functional approach using Enumerable#chunk:
ranges = [1, 2, 4, 5, 6, 7, 9, 13]
.enum_for(:chunk) # .chunk for Ruby >= 2.4
.with_index { |x, idx| x - idx }
.map { |_diff, group| [group.first, group.last] }
#=> [[1, 2], [4, 7], [9, 9], [13, 13]]
How it works: once indexed, consecutive elements in the array have the same x - idx, so we use that value to chunk (grouping of consecutive items) the input array. Finally we just need to take the first and last elements of each group to build the pairs.
5 Comments
cvshepherd
This looks really nice. Totally forgot about the new chunk method.
the Tin Man
And to take it one more step,
.map{ |min,max| min == max ? min : min .. max } will result in: [1..2, 4..7, 9, 13].the Tin Man
Or, change
[pairs.first[0], pairs.last[0]] to pairs.first[0] .. pairs.last[0] to get ranges in all positions: [1..2, 4..7, 9..9, 13..13].
Marc-André Lafortune
In Ruby 2.4, the
enum_for will no longer be necessary.Marc-André Lafortune
I also posted an even easier solution with
chunk_whileThis is almost straight from the enumerable#slice_before method documentation:
ar = [1,2,4,5,6,7,9,13]
prev = ar[0]
ar.slice_before{|e|prev,prev2 = e,prev; prev2.succ != e}.map{|a|a.first..a.last}
#=> [1..2, 4..7, 9..9, 13..13]
This should work with characters, dates, anything with a .succ method.
Comments
An even easier solution than @tokland's very nice one is using chunk_while:
xs.chunk_while { |a, b| a + 1 == b }.map do |seq|
[seq.first, seq.last]
end
Note: chunk_while was introduced in Ruby 2.3
answered Oct 6, 2016 at 3:51
Marc-André Lafortune
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Comments
Hmm, well, it's not tokland's masterpiece, but I think it may be a good straightforward solution...
[1,2,4,5,6,7,9,13].inject([]) do |m, v|
if m.last.to_a.last == v.pred
m[-1][-1] = v
else
m << [v, v]
end
m
end
Comments
Another approach
def summarize(x)
x.inject([]) do |acc, value|
if acc.last && acc.last[1] + 1 == value
acc.last[1] = value
acc
else
acc << [value,value]
end
end
end
Similar to Larsenal's method but using inject to manage the boring stuff.
