=head1 NAME
+X<data structure> X<complex data structure> X<struct>
perldsc - Perl Data Structures Cookbook
to develop and maintain--to put it mildly.
The 5.0 release of Perl let us have complex data structures. You
-may now write something like this and all of a sudden, you'd have a array
+may now write something like this and all of a sudden, you'd have an array
with three dimensions!
for $x (1 .. 10) {
How do you print it out? Why can't you say just C<print @AoA>? How do
you sort it? How can you pass it to a function or get one of these back
-from a function? Is is an object? Can you save it to disk to read
+from a function? Is it an object? Can you save it to disk to read
back later? How do you access whole rows or columns of that matrix? Do
all the values have to be numeric?
these types of data structures.
=head1 REFERENCES
+X<reference> X<dereference> X<dereferencing> X<pointer>
The most important thing to understand about all data structures in Perl
-- including multidimensional arrays--is that even though they might
one-dimensional. They can hold only scalar values (meaning a string,
number, or a reference). They cannot directly contain other arrays or
hashes, but instead contain I<references> to other arrays or hashes.
+X<multidimensional array> X<array, multidimensional>
-You can't use a reference to a array or hash in quite the same way that you
+You can't use a reference to an array or hash in quite the same way that you
would a real array or hash. For C or C++ programmers unused to
distinguishing between arrays and pointers to the same, this can be
confusing. If so, just think of it as the difference between a structure
memory. In Perl, you'll want to use the array constructor C<[]> or the
hash constructor C<{}> instead. Here's the right way to do the preceding
broken code fragments:
+X<[]> X<{}>
for $i (1..10) {
@array = somefunc($i);
Is it the same? Well, maybe so--and maybe not. The subtle difference
is that when you assign something in square brackets, you know for sure
it's always a brand new reference with a new I<copy> of the data.
-Something else could be going on in this new case with the C<@{$AoA[$i]}}>
+Something else could be going on in this new case with the C<@{$AoA[$i]}>
dereference on the left-hand-side of the assignment. It all depends on
whether C<$AoA[$i]> had been undefined to start with, or whether it
already contained a reference. If you had already populated @AoA with
=head1 CAVEAT ON PRECEDENCE
+X<dereference, precedence> X<dereferencing, precedence>
Speaking of things like C<@{$AoA[$i]}>, the following are actually the
same thing:
+X<< -> >>
$aref->[2][2] # clear
$$aref[2][2] # confusing
print $aref->[2][2]
=head1 DEBUGGING
+X<data structure, debugging> X<complex data structure, debugging>
+X<AoA, debugging> X<HoA, debugging> X<AoH, debugging> X<HoH, debugging>
+X<array of arrays, debugging> X<hash of arrays, debugging>
+X<array of hashes, debugging> X<hash of hashes, debugging>
Before version 5.002, the standard Perl debugger didn't do a very nice job of
printing out complex data structures. With 5.002 or above, the
types of data structures.
=head1 ARRAYS OF ARRAYS
+X<array of arrays> X<AoA>
-=head2 Declaration of a ARRAY OF ARRAYS
+=head2 Declaration of an ARRAY OF ARRAYS
@AoA = (
[ "fred", "barney" ],
[ "homer", "marge", "bart" ],
);
-=head2 Generation of a ARRAY OF ARRAYS
+=head2 Generation of an ARRAY OF ARRAYS
# reading from file
while ( <> ) {
# add to an existing row
push @{ $AoA[0] }, "wilma", "betty";
-=head2 Access and Printing of a ARRAY OF ARRAYS
+=head2 Access and Printing of an ARRAY OF ARRAYS
# one element
$AoA[0][0] = "Fred";
}
=head1 HASHES OF ARRAYS
+X<hash of arrays> X<HoA>
=head2 Declaration of a HASH OF ARRAYS
}
=head1 ARRAYS OF HASHES
+X<array of hashes> X<AoH>
-=head2 Declaration of a ARRAY OF HASHES
+=head2 Declaration of an ARRAY OF HASHES
@AoH = (
{
}
);
-=head2 Generation of a ARRAY OF HASHES
+=head2 Generation of an ARRAY OF HASHES
# reading from file
# format: LEAD=fred FRIEND=barney
$AoH[0]{pet} = "dino";
$AoH[2]{pet} = "santa's little helper";
-=head2 Access and Printing of a ARRAY OF HASHES
+=head2 Access and Printing of an ARRAY OF HASHES
# one element
$AoH[0]{lead} = "fred";
}
=head1 HASHES OF HASHES
+X<hass of hashes> X<HoH>
=head2 Declaration of a HASH OF HASHES
=head1 MORE ELABORATE RECORDS
+X<record> X<structure> X<struct>
=head2 Declaration of MORE ELABORATE RECORDS
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