Re^4: grep and dereferencing an array of arrays

The program is a self-grading multiple-choice testing environment. The teacher can enter an arbitrary number of questions, with four possible answers to each question. Only one of the answers may be correct. The program randomizes the questions and answers, so a student will never get the same test twice (and can't cheat using a scoring key). This example is a simple spelling test. Three of the answers are wrong ('W') and one is right ('R'):

==========
$VAR1 = [
          [
            'a',
            'W',
            'interupt'
          ],
          [
            'b',
            'R',
            'interrupt'
          ],
          [
            'c',
            'W',
            'innterupt'
          ],
          [
            'd',
            'W',
            'intterupt'
          ]
        ];

==========
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Since the answers have been randomized, the program has to match the entered answer letter ('a..d') to the 'W' or 'R' that is the second element of one of the elements of the $qablock. Only then can the actual answer be recorded for later scoring (since the answer 'b' has no lasting significance).

The reason that I removed the square brackets from the grep is because the element of $qablock that the grep is assigning should already be an anonymous array reference. But then I still had to use the brackets for the assignment in the foreach, so I tried it with brackets as well. Basically, I've been flailing in the hope of getting lucky....

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Re^5: grep and dereferencing an array of arrays by McA (Priest) on Sep 06, 2013 at 20:34 UTC
Ok, that puts some light on your problem. This may be your solution: `#!/usr/bin/env perl use strict; use warnings; use 5.010; use Data::Dumper; my $choices = [ [ 'a', 'W', 'interupt', ], [ 'b', 'R', 'interrupt', ], [ 'c', 'W', 'innterupt', ], [ 'd', 'W', 'intterupt', ] ]; my $answer = 'd'; # As we know that the answer matches only one choice # and we have exactly one matching answer. my $chosen_answer = (grep { $_->[0] eq $answer } @$choices)[0]; say Dumper($chosen_answer);` [download] McA	[reply] [d/l]
Re^6: grep and dereferencing an array of arrays by choroba (Cardinal) on Sep 06, 2013 at 21:04 UTC
Or, maybe more readable for some: `my ($chosen_answer) = grep { $_->[0] eq $answer } @$choices;` [download] لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ	[reply] [d/l]
Re^7: grep and dereferencing an array of arrays by McA (Priest) on Sep 06, 2013 at 21:12 UTC
I have to agree that this is more elegant and oakb asked for an elegant solution. Eily proposed almost the same a little earlier. Probably I can argue that my solution is more explicit. ;) Regards McA	[reply]
Re^5: grep and dereferencing an array of arrays by Marshall (Canon) on Sep 07, 2013 at 09:25 UTC
I am not sure what the objective is. However, a couple of possibilities come to mind... map{} can return a conditional thing...use () to return "nothing". See below. #!/usr/bin/perl -w use strict; my $VAR1 = [ [ 'a', 'W', 'interupt' ], [ 'b', 'R', 'interrupt' ], [ 'c', 'W', 'innterupt' ], [ 'd', 'W', 'intterupt' ] ]; print "Number of Questions: ", scalar @$VAR1, "\n"; #@$VAR1 produces a list of references to the arrays #The map selects the 2nd one of each array, index [1] #the grep in a scalar context counts them up print "Number right: ", scalar( grep{/r/i}map{@$_[1]}@$VAR1 ), "\n"; print "Number wrong: ", scalar( grep{/w/i}map{@$_[1]}@$VAR1 ), "\n"; #Maybe the question is which one is the "right" answer, a,b,c,d? print "\n"; print "correct answer is: ", map{@$_[1] =~ /r/i ? @$_[0]:()}@$VAR1; __END__ Number of Questions: 4 Number right: 1 Number wrong: 3 correct answer is: b Process completed successfully [download]	[reply] [d/l]