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Top Forums Shell Programming and Scripting awk - function to return permutations of n items out of m Post 303028497 by durden_tyler on Wednesday 9th of January 2019 01:38:08 PM
Old 01-09-2019
A very un-awk-like and more Perl-like script. Smilie

I added the sort routine because array iteration doesn't return the elements in order.
(Definitely not a good idea for large arrays.)

Note that the OP wants the results in an array for further processing in the same script.
I'm not sure how to retrieve the array elements in the order that they were inserted.
Maybe a forum member can suggest how to do so.

Code:
echo |
awk 'function generate_permutations(cs, item, n, k){
         if (k == 0){
             iter = iter + 1;
             arr[iter] = item;
             return;
         }
         for (i in cs){
             new_item = item""cs[i];
             generate_permutations(cs, new_item, n, k-1);
         }
     }
     {
          split("", arr, "");
          iter = 0;
          str = "a,b,c,d,e";
          n = split(str, charset, ",");
          k = 3;
          generate_permutations(charset, "", n, k);
          asort(arr);
          for (i=1; i <= iter; i++){
              printf "%s\n", arr[i];
          }
     }
    '


Last edited by durden_tyler; 01-09-2019 at 02:39 PM.. Reason: Too many blank lines added automatically between paragraphs.
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Perl::Critic::Policy::Variables::RequireNegativeIndices(User Contributed Perl DocumentPerl::Critic::Policy::Variables::RequireNegativeIndices(3pm)

NAME
Perl::Critic::Policy::Variables::RequireNegativeIndices - Negative array index should be used. AFFILIATION
This Policy is part of the core Perl::Critic distribution. DESCRIPTION
Conway points out that $arr[$#arr]; $arr[$#arr-1]; $arr[@arr-1]; $arr[@arr-2]; are equivalent to $arr[-1]; $arr[-2]; $arr[-1]; $arr[-2]; and the latter are more readable, performant and maintainable. The latter is because the programmer no longer needs to keep two variable names matched. This policy notices all of the simple forms of the above problem, but does not recognize any of these more complex examples: $some->[$data_structure]->[$#{$some->[$data_structure]} -1]; my $ref = @arr; $ref->[$#arr]; CONFIGURATION
This Policy is not configurable except for the standard options. AUTHOR
Chris Dolan <cdolan@cpan.org> COPYRIGHT
Copyright (c) 2006-2011 Chris Dolan. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. perl v5.14.2 2012-06-07 Perl::Critic::Policy::Variables::RequireNegativeIndices(3pm)
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