From: Dave Thomas <Dave@...>
Date: 2001-11-30T14:55:44+09:00
Subject: [ruby-talk:27029] Re: Help: factored sorting

Bil Kleb <W.L.Kleb@LaRC.NASA.Gov> writes:

> 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"]

Bil:

The sort part could be something like:

     a.map { |e|
       w, d = /([a-z]+)(\d+)/.match(e)[1,2]
       [ w, d.to_i, e]
     } .
     sort {|a,b| (a[0] <=> b[0]).nonzero? || a[1] <=> b[1] 
     } .
     map {|a,b,e| e}

> 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"] ]


I'd probably do this in three phases - it's a tad ugly..

     result = {}

     a.each { |e|
       w, d = /([a-z]+)(\d+)/.match(e)[1,2]
       (result[w] ||= []) << d.to_i
     } 

     result.each_value {|v| v.sort! }

     result =  result.to_a.sort.map { |letter,values|
       [ letter, values.map {|v| letter + v.to_s} ].flatten }

If you're flexible in the format of the result, there's also:

     result = {}

     a.each { |e|
       w, d = /([a-z]+)(\d+)/.match(e)[1,2]
       (result[w] ||= []) << d.to_i
     } 

     result.each_value {|v| v.sort! } .to_a.sort

The result's not quite what you asked for:

     [ [ "d", [3, 4, 33, 34] ], ["r", [16, 33, 34] ] ]



Regards


Dave