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Posted By

deepsoul on 07/11/11


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grep elem


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Short-circuited Perl grep

 / Published in: Perl
 

To check the existence of an element in a Perl array with specific properties, one tends to use grep. But this is inefficient because grep always checks each element. (Even in scalar context it returns the number of matching elements.) The following function aborts after the first find.

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  1. # Short-circuited grep in scalar context, which returns 1 if an element of the
  2. # passed list is evaluated to true by the anonymous subroutine, without
  3. # continuing after one has been found.
  4. # -> Anonymous test subroutine operating on $_
  5. #    List to test
  6. # <- 1 if an element matched, 0 otherwise
  7. sub shortgrep(&@)
  8. {
  9.   my $test= shift @_;
  10.   for (@_) {
  11.     return 1 if &$test;
  12.   }
  13.   return 0;
  14. }
  15.  
  16. # simple example usage, made possible by prototype:
  17. if( shortgrep { $_->{"entry"} eq "value" } @arrayofhashes ) {
  18.   ...
  19. }
  20. # "sub" and parentheses are still needed in more complex expressions:
  21. if( shortgrep(sub { $_ == 4 }, @ary) && $othercondition ) {
  22.   ...
  23. }

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