Heyo,
(1) Explains the (somewhat basic) mathematics behind the
"random number in range" question.
(2) Removes the srand stuff from the "random element from
array" question, and adds the one line idiom.
cheers,
--
Iain. <http://eh.org/~koschei/>
Index: perlfaq4.pod
===================================================================
RCS file: /cvs/public/perlfaq/perlfaq4.pod,v
retrieving revision 1.53
diff -u -r1.53 perlfaq4.pod
--- perlfaq4.pod 11 Nov 2003 02:23:32 -0000 1.53
+++ perlfaq4.pod 29 Nov 2003 03:21:53 -0000
@@ -362,9 +362,20 @@
=head2 How do I get a random number between X and Y?
-Use the following simple function. It selects a random integer between
-(and possibly including!) the two given integers, e.g.,
-C<random_int_in(50,120)>
+C<rand($x)> returns a number such that
+C<< 0 <= rand($x) < $x >>. Thus what you want to have perl
+figure out is a random number in the range from 0 to the
+difference between your I<X> and I<Y>.
+
+That is, to get a number between 10 and 15, inclusive, you
+want a random number between 0 and 5 that you can then add
+to 10.
+
+ my $number = 10 + int rand( 15-10+1 );
+
+Hence you derive the following simple function to abstract
+that. It selects a random integer between the two given
+integers (inclusive), For example: C<random_int_in(50,120)>.
sub random_int_in ($$) {
my($min, $max) = @_;
@@ -1481,16 +1492,11 @@
Use the rand() function (see L<perlfunc/rand>):
- # at the top of the program:
- srand; # not needed for 5.004 and later
-
- # then later on
$index = rand @array;
$element = $array[$index];
-Make sure you I<only call srand once per program, if then>.
-If you are calling it more than once (such as before each
-call to rand), you're almost certainly doing something wrong.
+Or, simply:
+ my $element = $array[ rand @array ];
=head2 How do I permute N elements of a list?
