FM / pod

/usr/share/perl5/pod

Name	Size	Mode	Actions
perl.pod	16667	0644	edit dl rm
perl56delta.pod	107201	0644	edit dl rm
perl58delta.pod	115165	0644	edit dl rm
perl561delta.pod	124713	0644	edit dl rm
perl581delta.pod	38060	0644	edit dl rm
perl582delta.pod	4470	0644	edit dl rm
perl583delta.pod	6335	0644	edit dl rm
perl584delta.pod	7363	0644	edit dl rm
perl585delta.pod	5889	0644	edit dl rm
perl586delta.pod	4651	0644	edit dl rm
perl587delta.pod	8357	0644	edit dl rm
perl588delta.pod	25281	0644	edit dl rm
perl589delta.pod	53904	0644	edit dl rm
perl5004delta.pod	56240	0644	edit dl rm
perl5005delta.pod	34283	0644	edit dl rm
perl5100delta.pod	55533	0644	edit dl rm
perl5101delta.pod	43888	0644	edit dl rm
perl5120delta.pod	89271	0644	edit dl rm
perl5121delta.pod	10141	0644	edit dl rm
perl5122delta.pod	9603	0644	edit dl rm
perl5123delta.pod	4100	0644	edit dl rm
perl5124delta.pod	3672	0644	edit dl rm
perl5125delta.pod	7683	0644	edit dl rm
perl5140delta.pod	144325	0644	edit dl rm
perl5141delta.pod	7966	0644	edit dl rm
perl5142delta.pod	6892	0644	edit dl rm
perl5143delta.pod	7760	0644	edit dl rm
perl5144delta.pod	6327	0644	edit dl rm
perl5160delta.pod	133651	0644	edit dl rm
perl5161delta.pod	6142	0644	edit dl rm
perl5162delta.pod	3594	0644	edit dl rm
perl5163delta.pod	4085	0644	edit dl rm
perl5180delta.pod	119429	0644	edit dl rm
perl5181delta.pod	6597	0644	edit dl rm
perl5182delta.pod	5335	0644	edit dl rm
perl5184delta.pod	4642	0644	edit dl rm
perl5200delta.pod	115698	0644	edit dl rm
perl5201delta.pod	10899	0644	edit dl rm
perl5202delta.pod	12509	0644	edit dl rm
perl5203delta.pod	9392	0644	edit dl rm
perl5220delta.pod	130963	0644	edit dl rm
perl5221delta.pod	10767	0644	edit dl rm
perl5222delta.pod	12629	0644	edit dl rm
perl5223delta.pod	8456	0644	edit dl rm
perl5224delta.pod	4460	0644	edit dl rm
perl5240delta.pod	64923	0644	edit dl rm
perl5241delta.pod	8215	0644	edit dl rm
perl5242delta.pod	4113	0644	edit dl rm
perl5243delta.pod	11428	0644	edit dl rm
perl5244delta.pod	4510	0644	edit dl rm
perl5260delta.pod	101835	0644	edit dl rm
perl5261delta.pod	7927	0644	edit dl rm
perl5262delta.pod	7880	0644	edit dl rm
perl5263delta.pod	7067	0644	edit dl rm
perl5280delta.pod	72113	0644	edit dl rm
perl5281delta.pod	4639	0644	edit dl rm
perl5282delta.pod	6200	0644	edit dl rm
perl5283delta.pod	5111	0644	edit dl rm
perl5300delta.pod	41281	0644	edit dl rm
perl5301delta.pod	5730	0644	edit dl rm
perl5302delta.pod	4682	0644	edit dl rm
perl5303delta.pod	4980	0644	edit dl rm
perl5320delta.pod	54601	0644	edit dl rm
perl5321delta.pod	7003	0644	edit dl rm
perlaix.pod	20438	0644	edit dl rm
perlamiga.pod	5749	0644	edit dl rm
perlandroid.pod	8222	0644	edit dl rm
perlapi.pod	493106	0644	edit dl rm
perlapio.pod	21336	0644	edit dl rm
perlartistic.pod	7010	0644	edit dl rm
perlbook.pod	8386	0644	edit dl rm
perlboot.pod	294	0644	edit dl rm
perlbot.pod	304	0644	edit dl rm
perlbs2000.pod	7994	0644	edit dl rm
perlcall.pod	56738	0644	edit dl rm
perlcheat.pod	4480	0644	edit dl rm
perlclib.pod	9607	0644	edit dl rm
perlcn.pod	4763	0644	edit dl rm
perlcommunity.pod	6983	0644	edit dl rm
perlcygwin.pod	27202	0644	edit dl rm
perldata.pod	49782	0644	edit dl rm
perldbmfilter.pod	4981	0644	edit dl rm
perldebguts.pod	42331	0644	edit dl rm
perldebtut.pod	22152	0644	edit dl rm
perldebug.pod	39383	0644	edit dl rm
perldelta.pod	7003	0644	edit dl rm
perldeprecation.pod	20825	0644	edit dl rm
perldiag.pod	296986	0644	edit dl rm
perldos.pod	10522	0644	edit dl rm
perldsc.pod	25614	0644	edit dl rm
perldtrace.pod	7959	0644	edit dl rm
perlebcdic.pod	84345	0644	edit dl rm
perlembed.pod	37569	0644	edit dl rm
perlexperiment.pod	7234	0644	edit dl rm
perlfork.pod	13355	0644	edit dl rm
perlform.pod	16608	0644	edit dl rm
perlfreebsd.pod	1623	0644	edit dl rm
perlfunc.pod	403777	0644	edit dl rm
perlgit.pod	29591	0644	edit dl rm
perlgov.pod	14481	0644	edit dl rm
perlgpl.pod	13815	0644	edit dl rm
perlguts.pod	162103	0644	edit dl rm
perlhack.pod	43157	0644	edit dl rm
perlhacktips.pod	57692	0644	edit dl rm
perlhacktut.pod	6153	0644	edit dl rm
perlhaiku.pod	1508	0644	edit dl rm
perlhist.pod	56164	0644	edit dl rm
perlhpux.pod	30609	0644	edit dl rm
perlhurd.pod	1994	0644	edit dl rm
perlintern.pod	83565	0644	edit dl rm
perlinterp.pod	33715	0644	edit dl rm
perlintro.pod	22135	0644	edit dl rm
perliol.pod	34804	0644	edit dl rm
perlipc.pod	71529	0644	edit dl rm
perlirix.pod	4415	0644	edit dl rm
perljp.pod	8431	0644	edit dl rm
perlko.pod	12208	0644	edit dl rm
perllexwarn.pod	355	0644	edit dl rm
perllinux.pod	2007	0644	edit dl rm
perllocale.pod	74112	0644	edit dl rm
perllol.pod	9580	0644	edit dl rm
perlmacos.pod	998	0644	edit dl rm
perlmacosx.pod	12124	0644	edit dl rm
perlmod.pod	26197	0644	edit dl rm
perlmodinstall.pod	10261	0644	edit dl rm
perlmodlib.pod	76348	0644	edit dl rm
perlmodstyle.pod	22588	0644	edit dl rm
perlmroapi.pod	3280	0644	edit dl rm
perlnetware.pod	6648	0644	edit dl rm
perlnewmod.pod	11037	0644	edit dl rm
perlnumber.pod	8353	0644	edit dl rm
perlobj.pod	35717	0644	edit dl rm
perlootut.pod	26757	0644	edit dl rm
perlop.pod	148888	0644	edit dl rm
perlopenbsd.pod	1224	0644	edit dl rm
perlopentut.pod	15223	0644	edit dl rm
perlos2.pod	93348	0644	edit dl rm
perlos390.pod	16527	0644	edit dl rm
perlos400.pod	4765	0644	edit dl rm
perlpacktut.pod	51370	0644	edit dl rm
perlperf.pod	49881	0644	edit dl rm
perlplan9.pod	5125	0644	edit dl rm
perlpod.pod	23076	0644	edit dl rm
perlpodspec.pod	68628	0644	edit dl rm
perlpolicy.pod	26562	0644	edit dl rm
perlport.pod	88693	0644	edit dl rm
perlpragma.pod	5176	0644	edit dl rm
perlqnx.pod	6673	0644	edit dl rm
perlre.pod	130817	0644	edit dl rm
perlreapi.pod	30245	0644	edit dl rm
perlrebackslash.pod	32285	0644	edit dl rm
perlrecharclass.pod	49707	0644	edit dl rm
perlref.pod	35432	0644	edit dl rm
perlreftut.pod	18826	0644	edit dl rm
perlreguts.pod	39301	0644	edit dl rm
perlrepository.pod	509	0644	edit dl rm
perlrequick.pod	19141	0644	edit dl rm
perlreref.pod	15590	0644	edit dl rm
perlretut.pod	122527	0644	edit dl rm
perlriscos.pod	1529	0644	edit dl rm
perlrun.pod	55980	0644	edit dl rm
perlsec.pod	27601	0644	edit dl rm
perlsecpolicy.pod	19450	0644	edit dl rm
perlsolaris.pod	29843	0644	edit dl rm
perlsource.pod	7132	0644	edit dl rm
perlstyle.pod	8734	0644	edit dl rm
perlsub.pod	74405	0644	edit dl rm
perlsymbian.pod	15344	0644	edit dl rm
perlsyn.pod	45138	0644	edit dl rm
perlsynology.pod	7960	0644	edit dl rm
perlthrtut.pod	46522	0644	edit dl rm
perltie.pod	39314	0644	edit dl rm
perltoc.pod	701800	0644	edit dl rm
perltodo.pod	372	0644	edit dl rm
perltooc.pod	294	0644	edit dl rm
perltoot.pod	294	0644	edit dl rm
perltrap.pod	10623	0644	edit dl rm
perltru64.pod	8492	0644	edit dl rm
perltw.pod	4463	0644	edit dl rm
perlunicode.pod	91353	0644	edit dl rm
perlunicook.pod	25658	0644	edit dl rm
perlunifaq.pod	13644	0644	edit dl rm
perluniintro.pod	38647	0644	edit dl rm
perluniprops.pod	441614	0644	edit dl rm
perlunitut.pod	7951	0644	edit dl rm
perlutil.pod	7291	0644	edit dl rm
perlvar.pod	82577	0644	edit dl rm
perlvms.pod	50823	0644	edit dl rm
perlvos.pod	3843	0644	edit dl rm
perlwin32.pod	40317	0644	edit dl rm

Edit: /usr/share/perl5/pod/perllol.pod (9580B)

=head1 NAME

perllol - Manipulating Arrays of Arrays in Perl

=head1 DESCRIPTION

=head2 Declaration and Access of Arrays of Arrays

The simplest two-level data structure to build in Perl is an array of
arrays, sometimes casually called a list of lists.  It's reasonably easy to
understand, and almost everything that applies here will also be applicable
later on with the fancier data structures.

An array of an array is just a regular old array @AoA that you can
get at with two subscripts, like C<$AoA[3][2]>.  Here's a declaration
of the array:

use 5.010;  # so we can use say()

# assign to our array, an array of array references
    @AoA = (
	   [ "fred", "barney", "pebbles", "bambam", "dino", ],
	   [ "george", "jane", "elroy", "judy", ],
	   [ "homer", "bart", "marge", "maggie", ],
    );
    say $AoA[2][1];
  bart

Now you should be very careful that the outer bracket type
is a round one, that is, a parenthesis.  That's because you're assigning to
an @array, so you need parentheses.  If you wanted there I<not> to be an @AoA,
but rather just a reference to it, you could do something more like this:

# assign a reference to array of array references
    $ref_to_AoA = [
	[ "fred", "barney", "pebbles", "bambam", "dino", ],
	[ "george", "jane", "elroy", "judy", ],
	[ "homer", "bart", "marge", "maggie", ],
    ];
    say $ref_to_AoA->[2][1];
  bart

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.  $ref_to_AoA is a reference to an
array, whereas @AoA is an array proper.  Likewise, C<$AoA[2]> is not an
array, but an array ref.  So how come you can write these:

$AoA[2][2]
    $ref_to_AoA->[2][2]

instead of having to write these:

$AoA[2]->[2]
    $ref_to_AoA->[2]->[2]

Well, that's because the rule is that on adjacent brackets only (whether
square or curly), you are free to omit the pointer dereferencing arrow.
But you cannot do so for the very first one if it's a scalar containing
a reference, which means that $ref_to_AoA always needs it.

=head2 Growing Your Own

That's all well and good for declaration of a fixed data structure,
but what if you wanted to add new elements on the fly, or build
it up entirely from scratch?

First, let's look at reading it in from a file.  This is something like
adding a row at a time.  We'll assume that there's a flat file in which
each line is a row and each word an element.  If you're trying to develop an
@AoA array containing all these, here's the right way to do that:

while (<>) {
	@tmp = split;
	push @AoA, [ @tmp ];
    }

You might also have loaded that from a function:

for $i ( 1 .. 10 ) {
	$AoA[$i] = [ somefunc($i) ];
    }

Or you might have had a temporary variable sitting around with the
array in it.

for $i ( 1 .. 10 ) {
	@tmp = somefunc($i);
	$AoA[$i] = [ @tmp ];
    }

It's important you make sure to use the C<[ ]> array reference
constructor.  That's because this wouldn't work:

$AoA[$i] = @tmp;   # WRONG!

The reason that doesn't do what you want is because assigning a
named array like that to a scalar is taking an array in scalar
context, which means just counts the number of elements in @tmp.

If you are running under C<use strict> (and if you aren't, why in
the world aren't you?), you'll have to add some declarations to
make it happy:

use strict;
    my(@AoA, @tmp);
    while (<>) {
	@tmp = split;
	push @AoA, [ @tmp ];
    }

Of course, you don't need the temporary array to have a name at all:

while (<>) {
	push @AoA, [ 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:

my (@AoA, $i, $line);
    for $i ( 0 .. 10 ) {
	$line = <>;
	$AoA[$i] = [ split " ", $line ];
    }

or even just

my (@AoA, $i);
    for $i ( 0 .. 10 ) {
	$AoA[$i] = [ split " ", <> ];
    }

You should in general be leery of using functions that could
potentially return lists in scalar context without explicitly stating
such.  This would be clearer to the casual reader:

my (@AoA, $i);
    for $i ( 0 .. 10 ) {
	$AoA[$i] = [ split " ", scalar(<>) ];
    }

If you wanted to have a $ref_to_AoA variable as a reference to an array,
you'd have to do something like this:

while (<>) {
	push @$ref_to_AoA, [ split ];
    }

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 (1 .. 10) {
	for $y (1 .. 10) {
	    $AoA[$x][$y] = func($x, $y);
	}
    }

for $x ( 3, 7, 9 ) {
	$AoA[$x][20] += func2($x);
    }

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.

If you wanted just to append to a row, you'd have
to do something a bit funnier looking:

# add new columns to an existing row
    push @{ $AoA[0] }, "wilma", "betty";   # explicit deref

=head2 Access and Printing

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 $AoA[0][0];

If you want to print the whole thing, though, you can't
say

print @AoA;		# WRONG

because you'll get just references listed, and perl will never
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.

for $aref ( @AoA ) {
	say "\t [ @$aref ],";
    }

If you wanted to keep track of subscripts, you might do this:

for $i ( 0 .. $#AoA ) {
	say "\t elt $i is [ @{$AoA[$i]} ],";
    }

or maybe even this.  Notice the inner loop.

for $i ( 0 .. $#AoA ) {
	for $j ( 0 .. $#{$AoA[$i]} ) {
	    say "elt $i $j is $AoA[$i][$j]";
	}
    }

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 .. $#AoA ) {
	$aref = $AoA[$i];
	for $j ( 0 .. $#{$aref} ) {
	    say "elt $i $j is $AoA[$i][$j]";
	}
    }

Hmm... that's still a bit ugly.  How about this:

for $i ( 0 .. $#AoA ) {
	$aref = $AoA[$i];
	$n = @$aref - 1;
	for $j ( 0 .. $n ) {
	    say "elt $i $j is $AoA[$i][$j]";
	}
    }

When you get tired of writing a custom print for your data structures,
you might look at the standard L<Dumpvalue> or L<Data::Dumper> modules.
The former is what the Perl debugger uses, while the latter generates
parsable Perl code.  For example:

use v5.14;     # using the + prototype, new to v5.14

sub show(+) {
	require Dumpvalue;
	state $prettily = new Dumpvalue::
			    tick        => q("),
			    compactDump => 1,  # comment these two lines
                                               # out
			    veryCompact => 1,  # if you want a bigger
                                               # dump
			;
	dumpValue $prettily @_;
 }

# Assign a list of array references to an array.
 my @AoA = (
	   [ "fred", "barney" ],
	   [ "george", "jane", "elroy" ],
	   [ "homer", "marge", "bart" ],
 );
 push @{ $AoA[0] }, "wilma", "betty";
 show @AoA;

will print out:

0  0..3  "fred" "barney" "wilma" "betty"
    1  0..2  "george" "jane" "elroy"
    2  0..2  "homer" "marge" "bart"

Whereas if you comment out the two lines I said you might wish to,
then it shows it to you this way instead:

0  ARRAY(0x8031d0)
       0  "fred"
       1  "barney"
       2  "wilma"
       3  "betty"
    1  ARRAY(0x803d40)
       0  "george"
       1  "jane"
       2  "elroy"
    2  ARRAY(0x803e10)
       0  "homer"
       1  "marge"
       2  "bart"

=head2 Slices

If you want to get at a slice (part of a row) in a multidimensional
array, you're going to have to do some fancy subscripting.  That's
because while we have a nice synonym for single elements via the
pointer arrow for dereferencing, no such convenience exists for slices.

Here's how to do one operation using a loop.  We'll assume an @AoA
variable as before.

@part = ();
    $x = 4;
    for ($y = 7; $y < 13; $y++) {
	push @part, $AoA[$x][$y];
    }

That same loop could be replaced with a slice operation:

@part = @{$AoA[4]}[7..12];

or spaced out a bit:

@part = @{ $AoA[4] } [ 7..12 ];

But as you might well imagine, this can get pretty rough on the reader.

Ah, but what if you wanted a I<two-dimensional slice>, such as having
$x run from 4..8 and $y run from 7 to 12?  Hmm... here's the simple way:

@newAoA = ();
    for ($startx = $x = 4; $x <= 8; $x++) {
	for ($starty = $y = 7; $y <= 12; $y++) {
	    $newAoA[$x - $startx][$y - $starty] = $AoA[$x][$y];
	}
    }

We can reduce some of the looping through slices

for ($x = 4; $x <= 8; $x++) {
	push @newAoA, [ @{ $AoA[$x] } [ 7..12 ] ];
    }

If you were into Schwartzian Transforms, you would probably
have selected map for that

@newAoA = map { [ @{ $AoA[$_] } [ 7..12 ] ] } 4 .. 8;

Although if your manager accused you of seeking job security (or rapid
insecurity) through inscrutable code, it would be hard to argue. :-)
If I were you, I'd put that in a function:

@newAoA = splice_2D( \@AoA, 4 => 8, 7 => 12 );
    sub splice_2D {
	my $lrr = shift; 	# ref to array of array refs!
	my ($x_lo, $x_hi,
	    $y_lo, $y_hi) = @_;

return map {
	    [ @{ $lrr->[$_] } [ $y_lo .. $y_hi ] ]
	} $x_lo .. $x_hi;
    }

=head1 SEE ALSO

L<perldata>, L<perlref>, L<perldsc>

=head1 AUTHOR

Tom Christiansen <F<tchrist@perl.com>>

Last update: Tue Apr 26 18:30:55 MDT 2011

cmd: