Re: [PATCH mg.c gv.c and others] ${^TAINT}

[p5sagit/p5-mst-13.2.git] / pod / perlfaq4.pod

diff --git a/pod/perlfaq4.pod b/pod/perlfaq4.pod
index 08f23f0..72eb8d8 100644 (file)
--- a/pod/perlfaq4.pod
+++ b/pod/perlfaq4.pod
@@ -1,6 +1,6 @@
 =head1 NAME
 
-perlfaq4 - Data Manipulation ($Revision: 1.49 $, $Date: 1999/05/23 20:37:49 $)
+perlfaq4 - Data Manipulation ($Revision: 1.2 $, $Date: 2001/09/26 15:42:12 $)
 
 =head1 DESCRIPTION
 
@@ -583,7 +583,7 @@ To make the first letter of each word upper case:
 
 This has the strange effect of turning "C<don't do it>" into "C<Don'T
 Do It>".  Sometimes you might want this.  Other times you might need a
-more thorough solution (Suggested by brian d.  foy):
+more thorough solution (Suggested by brian d foy):
 
     $string =~ s/ (
                  (^\w)    #at the beginning of the line
@@ -1198,14 +1198,21 @@ lists, or you could just do something like this with an array:
 
 =head2 How do I shuffle an array randomly?
 
-Use this:
+If you either have Perl 5.8.0 or later installed, or if you have
+Scalar-List-Utils 1.03 or later installed, you can say:
+
+        use List::Util 'shuffle';
+
+       @shuffled = shuffle(@list);
+
+If not, you can use this:
 
     # fisher_yates_shuffle( \@array ) : 
     # generate a random permutation of @array in place
     sub fisher_yates_shuffle {
         my $array = shift;
-        my $i;
-        for ($i = @$array; --$i; ) {
+        my $i = @$array;
+        while (--$i) {
             my $j = int rand ($i+1);
             @$array[$i,$j] = @$array[$j,$i];
         }
@@ -1213,6 +1220,10 @@ Use this:
 
     fisher_yates_shuffle( \@array );    # permutes @array in place
 
+Note that the above implementation shuffles an array in place,
+unlike the List::Util::shuffle() which takes a list and returns
+a new shuffled list.
+
 You've probably seen shuffling algorithms that work using splice,
 randomly picking another element to swap the current element with
 
@@ -1291,6 +1302,12 @@ in the permute() function should work on any list:
        }
     }
 
+Unfortunately, this algorithm is very inefficient. The Algorithm::Permute
+module from CPAN runs at least an order of magnitude faster. If you don't
+have a C compiler (or a binary distribution of Algorithm::Permute), then
+you can use List::Permutor which is written in pure Perl, and is still
+several times faster than the algorithm above.
+
 =head2 How do I sort an array by (anything)?
 
 Supply a comparison function to sort() (described in L<perlfunc/sort>):