From: Bil Kleb <W.L.Kleb@...>
Date: 2001-11-30T14:16:18+09:00
Subject: [ruby-talk:27026] Help: factored sorting

I have an array of strings,

a = ["d3", "d33", "d4", "r16", "r33", "d34", "r34"]

which I'd like to sort by both the numerical suffix and by
the alphabetic prefix, i.e., I'd like the result,

 ["d3", "d4", "d33", "d34", "r16", "r33", "r34"]

or, even better would be an array of two prefix-keyed
sub arrays that I could exploit with the assoc method,
viz,

 [ ["d", "d3", "d4", "d33", "d34"], ["r", "r16", "r33", "r34"] ]

A straight lexiconic sort, e.g., a.sort, gives all
the d's followed by the r's, but does not yield the
desired numerical ordering because the single and double
digit integer suffixes, viz,

 ["d3", "d33", "d34", "d4", "r16", "r33", "r34"] 

Meanwhile an (inept?) numerical sorting, e.g.,

a.sort { |a,b| a.scan(/\d+/).to_s.to_i <=> b.scan(/\d+/).to_s.to_i }

gives the desired numerical sequence, but mixes the d and r prefixes
together, viz,

 ["d3", "d4", "r16", "d33", "r33", "d34", "r34"]

Is there an elegant way to accomplish this type of factored sort
without resorting to padding the digit suffix or similar convoluted
mechanics?

TIA,
--
Bil <http://abweb.larc.nasa.gov/~kleb/>