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Re^2: Equality checking for strings AND numbers

by mjscott2702 (Pilgrim)
on Jul 15, 2007 at 23:41 UTC ( #626749=note: print w/replies, xml ) Need Help??


in reply to Re: Equality checking for strings AND numbers
in thread Equality checking for strings AND numbers

The problems here is that all of the numbers (ints and reals) do have different precisions - 10.0 and 10.00 are numerically equivalent, but are different when treated as strings.
  • Comment on Re^2: Equality checking for strings AND numbers

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Re^3: Equality checking for strings AND numbers
by Anonymous Monk on Jul 16, 2007 at 03:00 UTC
    Check this page out, It has tests to find variables types, and how to convert them. You can test if a value is an int, if it is convert it to a real and then do the comparison.

    http://search.cpan.org/~dwheeler/Data-Types-0.06/lib/Data/Types.pm.

    With this you should be able to get it to at least the same variable type. If both become float types and and you compare 10.0 to 10.00, you should end up with equality... Another though that you can do is set up a tolerance for precision on number comparisons;

    Instead of if a == b

    do if (absolute value of (a - b)) > .0001 then .....

    Just some thoughts. I personally haven't done a lot with Perl yet.

Re^3: Equality checking for strings AND numbers
by DrHyde (Prior) on Jul 17, 2007 at 09:31 UTC

    I'd argue that if you're bothering to mention precision at all, then 10.0 != 10.00.

    10.0 is really "somewhere between 9.95 and 10.05", and 10.00 is really "somewhere between 9.995 and 10.005". So if your 10.0 is really 9.97, it can't possibly be equal to 10.00.

      I guess it all comes down to how precise you want equality test to be in this program. If you want exact on the money the only way to get that I have ever seen is to do a direct string comparison as mentioned above. In this case 10.0 != 10.00. The reply to this suggestion before was that (10.0 == 10.00) evaluated to true. So it comes down to the basic question that has been asked throughout this post

      "How Precise do you want the numeric comparison to be?"

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