ruby - Array of indexes to array of ranges

Question

Ranges in ruby are pretty cool. I end up with arrays such as this:

geneRanges = [(234..25), (500..510), (1640..1653)]

And subsequently have to remove bits of them. For that I:

genePositions = geneRanges.collect {|range| range.entries }.flatten
=> [500, 501, 502, 503, 504, 505, 506, 507, 508, 509, 510, 1640, 1641, 1642, 1643, 1644, 1645, 1646, 1647, 1648, 1649, 1650, 1651, 1652, 1653]

They get manipulated, so some numbers get excluded, and others may be added. I may end up with this:

[505, 506, 507, 600, 601, 602, 603, 1643, 1644, 1645, 1646, 1647, 1648, 1649, 1650, 1651, 1652, 1653, 1654]

How can I convert this back into a compact array of ranges? It seems that the inverse function should exist? I would expect it to return something like this:

[(505..507), (600..603), (1643..1654)]

Thanks!

Answer 1

(New and improved. Stays fresh in your refrigerator for up to two weeks!):

a = [1, 2, 3, 10, 11, 20, 20, 4]

ranges = a.sort.uniq.inject([]) do |spans, n|
  if spans.empty? || spans.last.last != n - 1
    spans + [n..n]
  else
    spans[0..-2] + [spans.last.first..n]
  end
end

p ranges    # [1..4, 10..11, 20..20]