On Thu, 26 Sep 2002, Toby Stuart wrote:
> $a = 1;
> @b = (1,2,3,4);
> $i = grep(/$a/,@b);
> print "in array" if $i > 0;
This is both an incorrect and ineffecient solution
Incorrect because you are checking for the pattern 1 in all the elements
of @b. If @b were to be (2, 3, 11, 12) your soln will still say "in array".
The check should be $a == $_
Ineffecient because you are using grep for this purpose. If @b were to be
(1, 2, 3, 4) just checking the first element should return a true, but
with grep you will check all the elements no matter what.
These are my comments to the OP, for an "is it present" kind of operation
a hash is a better option. If you insist on an array, loop through the
array and last (perldoc -f last) out of the loop when the check succeeds.
If the array is sorted do a binary search on it.
If you don't mind hashes you can do this
my %num_hash;
@num_hash{@b} = (); # This is a hash slice
if (exists($num_hash{$a})) { # perldoc -f exist
print "in array\n";
}
You can use this if there will be infrequent "is it present" operations.
If not do away with the array and use a hash with the array elements as
the hash keys.
Also please don't declare scalars as $a, perldoc -f sort for more details
Read through
perldoc -q 'How can I tell whether a certain element is con-tained in a list or array?'
>
>
>
> > -----Original Message-----
> > From: Alex Cheung Tin Ka [mailto:[EMAIL PROTECTED]]
> > Sent: Thursday, September 26, 2002 5:00 PM
> > To: [EMAIL PROTECTED]
> > Subject: how to check variable in list
> >
> >
> > Dear All,
> > I would like to know how to check whether a variable
> > exists in an array
> > here is my code
> >
> > $a = 1;
> > @b = (1,2,3,4);
> >
> > Regards.
> > Alex
> >
>
>
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