From: Christopher Dicely <cmdicely@...>
Date: 2009-04-04T00:03:58+09:00
Subject: Re: An array problem

On Thu, Apr 2, 2009 at 9:23 AM, Robert Klemme
<shortcutter@googlemail.com> wrote:
> 2009/4/2 George George <george.githinji@gmail.com>:
>
>> i have a 3 arrays(A,B,C) which are results of some analysis.
>
> I'd rather not make those constants (A,B,C) because they aren't as you stated.
>
>> Array A has all members such that array B and C are actually subsets of
>> A. The order of elements in array A is important.
>>
>> What i want is to list all members of A such that if an element in A is
>> a found in B or C produce a report such as
>>
>> element1 -b
>> element2 -b
>> element3 -c
>> element4 -b
>> ....
>>
>> where the order of elements in the report is as was in array A.
>>
>>
>> my rather silly implentation was
>> A.each do |element|
>>  if B.detect(element)
>>    puts "#{element}- b"
>>  end
>> end
>>
>> however i don't think this is the right way to do it since it does not
>> give me the designed result. Can someone help me spot the bug?
>
> You want #include? instead of #detect:
>
> a.each do |el|
>  case
>    when b.include? el
>      puts "#{el} -b"
>    when c.include? el
>      puts "#{el} -c"
>  end
> end

Neither ruby 1.8.6 (in IRB) or Jruby 1.2.0 (in jirb_swing) likes this
without parenthesizing the argument to include? in the when clauses,
but a bigger problem is that if both b and c include a value it will
only print that b did, since when clauses are exclusive.

If its not essential to preprocess the arrays as in your second
approach, the following works:

puts a.map { |el|
  {b=>'b',c=>'c'}.map { |arr, label|
    "#{el} -#{label}" if arr.include?(el)
  }
}.flatten.compact