in reply to Re: All array elements the same?
in thread All array elements the same?

Okay, you threw me on this one. Could someone please explain the above code. I am completely lost!

J. J. Horner
Linux, Perl, Apache, Stronghold, Unix
jhorner@knoxlug.org http://www.knoxlug.org/

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RE: RE: Re: All array elements the same?
by davorg (Chancellor) on Aug 01, 2000 at 20:39 UTC

    It does the job tho' :)

    Ok. With comments...

    # define a hash to count the unique elements in @arr my %check; # @check{@arr} is a hash slice. It gives to all of the # values in %check where the key is an element from @arr. # This is a list and it's also an lvalue (i.e. you can # assign values to it. # # (1) x @arr (and I've corrected this from the original # version. Uses the 'x' operator as a list constructor. # In a list context it creates a list containing its # left operand repeated the number of times given by # the right operand (which is a scalar). @arr in a scalar # context gives the number of elements in @arr. Hence # we get a list containing scalar(@arr) 1s. # # We then assign this list to the list of lvalues created # by @check{@arr}. This assigns a 1 to each value associated # with a key found %check. The keys of %check are given by # @arr, therefore we effectively create a key/value pair # in %check for each element of @arr where the key is the # element of @arr and the value is 1. If any element of # @arr occurs multiple times we assign to the relevant # value in %check multiple times. # # We can then use 'keys' to extract this list of keys. If # all the elements of @arr are the same the list of keys # in %create only has one element. @check{@arr} = (1) x @arr; print "All the same" if keys %check == 1;

    Does that help?</code> --
    <http://www.dave.org.uk>

    European Perl Conference - Sept 22/24 2000, ICA, London
    <http://www.yapc.org/Europe/>

RE:(3) All array elements the same? (Code explained)
by Russ (Deacon) on Aug 01, 2000 at 20:34 UTC
    He's putting all the elements of the array into a hash, using a hash slice @check{@arr} = @arr x 1;

    Then, if there is only one key, all the values must have been identical.

    @check{@arr} is the "keys" part of the slice, and @arr x 1 just gives us the correct number of "values."

    Voila! A list of the unique elements of @arr (in keys %check). If there is only one unique element, then they are all the same. Two problems solved for the price (two lines, in this case) of one. :-)

    Russ
    Brainbench 'Most Valuable Professional' for Perl

      I see now. Apparently I don't have enough caffeine.

      It was the @hash{@array} thing that threw me. Don't see that often and have never used it.

      J. J. Horner
      Linux, Perl, Apache, Stronghold, Unix
      jhorner@knoxlug.org http://www.knoxlug.org/