"Paul Archer" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> Is there any (quick and easy) way to get a reverse range, like (10..1),
> rather than a standard (1..10)? The catch is to *not* use 'reverse'.
> I'm teaching Sun's perl course this week (DTP-250), and we were talking
> about working on arrays. The book had an exercise that had the student
> reverse an array by using pop (or shift, I don't remember). That section
is
> before we talk about 'reverse', and I thought you'd be able to do it like:
> @array[0 .. $#array] = @array[$#array .. 0]
> ...but of course, having the range count down doesn't work.
>
> Paul
Reverse an array without using reverse():
with an array slice and map():
[EMAIL PROTECTED] trwww]$ perl
@array = ( 1 .. 5 );
@array = @array[ map abs(), -$#array .. 0 ];
print( join("\n", @array), "\n" );
Ctrl-D
5
4
3
2
1
using splice(), pop(), and for():
[EMAIL PROTECTED] trwww]$ perl
@array = ( 1 .. 5 );
splice( @array, $_, 0, pop @array ) for ( 0 .. $#array );
print( join("\n", @array), "\n" );
Ctrl-D
5
4
3
2
1
or the C way (but skipping the temporary variable):
[EMAIL PROTECTED] perl]$ perl
@array = ( 1 .. 5 );
for ( $a = 0, $z = $#array; $a < $z; $a++, $z-- ) {
( $array[$a], $array[$z] ) = ( $array[$z], $array[$a] );
# @array[ $a, $z ] = @array[ $z, $a ]; # works too
}
print( join("\n", @array), "\n" );
Ctrl-D
5
4
3
2
1
perl is soooo cool.
Todd W.
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