a declaration of the array:
# assign to our array a list of list references
- @LoL = (
+ @LoL = (
[ "fred", "barney" ],
[ "george", "jane", "elroy" ],
[ "homer", "marge", "bart" ],
print $ref_to_LoL->[2][2];
-Notice that the outer bracket type has changed, and so our access syntax
+Notice that the outer bracket type has changed, and so our access syntax
has also changed. That's because unlike C, in perl you can't freely
-interchange arrays and references thereto. $ref_to_LoL is a reference to an
-array, whereas @LoL is an array proper. Likewise, C<$LoL[2]> is not an
+interchange arrays and references thereto. $ref_to_LoL is a reference to an
+array, whereas @LoL is an array proper. Likewise, C<$LoL[2]> is not an
array, but an array ref. So how come you can write these:
$LoL[2][2]
while (<>) {
@tmp = split;
push @LoL, [ @tmp ];
- }
+ }
You might also have loaded that from a function:
}
Or you might have had a temporary variable sitting around with the
-list in it.
+list in it.
for $i ( 1 .. 10 ) {
@tmp = somefunc($i);
$LoL[$i] = @tmp;
-You see, assigning a named list like that to a scalar just counts the
-number of elements in @tmp, which probably isn't what you want.
+You see, assigning a named list like that to a scalar just counts the
+number of elements in @tmp, which probably isn't what you want.
If you are running under C<use strict>, you'll have to add some
declarations to make it happy:
while (<>) {
@tmp = split;
push @LoL, [ @tmp ];
- }
+ }
Of course, you don't need the temporary array to have a name at all:
while (<>) {
push @LoL, [ split ];
- }
+ }
You also don't have to use push(). You could just make a direct assignment
if you knew where you wanted to put it:
for $i ( 0 .. 10 ) {
$line = <>;
$LoL[$i] = [ split ' ', $line ];
- }
+ }
or even just
my (@LoL, $i);
for $i ( 0 .. 10 ) {
$LoL[$i] = [ split ' ', <> ];
- }
+ }
You should in general be leery of using potential list functions
-in a scalar context without explicitly stating such.
+in a scalar context without explicitly stating such.
This would be clearer to the casual reader:
my (@LoL, $i);
for $i ( 0 .. 10 ) {
$LoL[$i] = [ split ' ', scalar(<>) ];
- }
+ }
If you wanted to have a $ref_to_LoL variable as a reference to an array,
you'd have to do something like this:
while (<>) {
push @$ref_to_LoL, [ split ];
- }
+ }
Actually, if you were using strict, you'd have to declare not only
$ref_to_LoL as you had to declare @LoL, but you'd I<also> having to
-initialize it to a reference to an empty list. (This was a bug in 5.001m
-that's been fixed for the 5.002 release.)
+initialize it to a reference to an empty list. (This was a bug in
+perl version 5.001m that's been fixed for the 5.002 release.)
my $ref_to_LoL = [];
while (<>) {
push @$ref_to_LoL, [ split ];
- }
+ }
Ok, now you can add new rows. What about adding new columns? If you're
dealing with just matrices, it's often easiest to use simple assignment:
for $x ( 3, 7, 9 ) {
$LoL[$x][20] += func2($x);
- }
+ }
-It doesn't matter whether those elements are already
+It doesn't matter whether those elements are already
there or not: it'll gladly create them for you, setting
intervening elements to C<undef> as need be.
=head1 Access and Printing
-Now it's time to print your data structure out. How
+Now it's time to print your data structure out. How
are you going to do that? Well, if you want only one
of the elements, it's trivial:
print @LoL; # WRONG
because you'll get just references listed, and perl will never
-automatically dereference things for you. Instead, you have to
+automatically dereference things for you. Instead, you have to
roll yourself a loop or two. This prints the whole structure,
using the shell-style for() construct to loop across the outer
-set of subscripts.
+set of subscripts.
for $aref ( @LoL ) {
print "\t [ @$aref ],\n";
}
}
-As you can see, it's getting a bit complicated. That's why
+As you can see, it's getting a bit complicated. That's why
sometimes is easier to take a temporary on your way through:
for $i ( 0 .. $#LoL ) {
variable as before.
@part = ();
- $x = 4;
+ $x = 4;
for ($y = 7; $y < 13; $y++) {
push @part, $LoL[$x][$y];
- }
+ }
That same loop could be replaced with a slice operation:
for ($starty = $y = 7; $x <= 12; $y++) {
$newLoL[$x - $startx][$y - $starty] = $LoL[$x][$y];
}
- }
+ }
-We can reduce some of the looping through slices
+We can reduce some of the looping through slices
for ($x = 4; $x <= 8; $x++) {
push @newLoL, [ @{ $LoL[$x] } [ 7..12 ] ];
@newLoL = splice_2D( \@LoL, 4 => 8, 7 => 12 );
sub splice_2D {
my $lrr = shift; # ref to list of list refs!
- my ($x_lo, $x_hi,
+ my ($x_lo, $x_hi,
$y_lo, $y_hi) = @_;
- return map {
- [ @{ $lrr->[$_] } [ $y_lo .. $y_hi ] ]
+ return map {
+ [ @{ $lrr->[$_] } [ $y_lo .. $y_hi ] ]
} $x_lo .. $x_hi;
- }
+ }
=head1 SEE ALSO
=head1 AUTHOR
-Tom Christiansen E<lt>F<tchrist@perl.com>E<gt>
+Tom Christiansen <F<tchrist@perl.com>>
Last udpate: Sat Oct 7 19:35:26 MDT 1995
projects / p5sagit/p5-mst-13.2.git / blobdiff