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Re: Multiple Permutation handling

by Laurent_R (Parson)
on Mar 03, 2013 at 23:01 UTC ( #1021537=note: print w/ replies, xml ) Need Help??


in reply to Multiple Permutation handling

Hi Midget

as noted above, I have suggested yesterday four nested foreach loops in my answer to your cross post on the DevShed forum:

foreach my $s1 (@set1) { foreach my $s2 (@set2) { foreach my $s3 (@sizes) { foreach my $s4 (@colors) { print "$s1$s2$s3$s4\n"; } } } }

And I believe it is probably the best solution: clean, easy to read, easy to understand and efficient.

For the fun of it, however, let me suggest a kind of "Schwartzian" solution, which could also be called a "Lisp written in Perl" solution (or Scheme, or Haskell, or whatever functional language written in Perl):

my @sku = qw/SKU1 SKU2 SKU3/; my @tslh = qw/t s l h/; my @colors = qw/BLU GRN WHT BLK /; my @sizes = qw / S M L XL 2X /; print map { $col = $_; map { $siz = $_; map {$a1 =$_; map "$_ $a1 $siz + $col\n", @sku;} @tslh} @sizes } @colors;

(I have added spaces between the fields to make the output easier to read.) This prints (I copy only the beginning and the end of the 240-line printout):

SKU1 t S BLU SKU2 t S BLU SKU3 t S BLU SKU1 s S BLU SKU2 s S BLU ... SKU3 l 2X BLK SKU1 h 2X BLK SKU2 h 2X BLK SKU3 h 2X BLK

The beauty (and fun) of this solution is of course that it holds in just one line of code (in pure Perl, without using a module to do the work behind the scene).

There are a number of downsides to this solution, however: first, it is far less easy to understand, it is actually hardly readable. Even though I just wrote it, I am not sure how I would explain it to make it clearly understandable.

To tell the truth, it was also a bit complicated for me to write it: it took me about 3 minutes to write the foreach nested loops above (which I did not even need to test), and and it took me slightly more than half an hour to get the nested map function calls to work correctly. So, in brief, this was just for the fun, I do not recommend this solution.


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Re^2: Multiple Permutation handling
by ggoebel (Sexton) on Mar 04, 2013 at 13:57 UTC
    Everyone knows that debugging is twice as hard as writing a program in the first place. So if you're as clever as you can be when you write it, how will you ever debug it?
    -- Brian Kernighan, "The Elements of Programming Style", 2nd edition, chapter 2
    

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