prior to its 5.0 release was complex data structures. Even without direct
language support, some valiant programmers did manage to emulate them, but
it was hard work and not for the faint of heart. You could occasionally
-get away with the C<$m{$LoL,$b}> notation borrowed from I<awk> in which the
-keys are actually more like a single concatenated string C<"$LoL$b">, but
+get away with the C<$m{$AoA,$b}> notation borrowed from B<awk> in which the
+keys are actually more like a single concatenated string C<"$AoA$b">, but
traversal and sorting were difficult. More desperate programmers even
hacked Perl's internal symbol table directly, a strategy that proved hard
to develop and maintain--to put it mildly.
may now write something like this and all of a sudden, you'd have a array
with three dimensions!
- for $x (1 .. 10) {
- for $y (1 .. 10) {
- for $z (1 .. 10) {
- $LoL[$x][$y][$z] =
- $x ** $y + $z;
+ my @AoA;
+ for my $x (1 .. 10) {
+ for my $y (1 .. 10) {
+ for my $z (1 .. 10) {
+ $AoA[$x][$y][$z] = $x ** $y + $z;
}
}
}
Alas, however simple this may appear, underneath it's a much more
elaborate construct than meets the eye!
-How do you print it out? Why can't you say just C<print @LoL>? How do
+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
back later? How do you access whole rows or columns of that matrix? Do
purloin a drop-in example from here.
Let's look at each of these possible constructs in detail. There are separate
-documents on each of the following:
+sections on each of the following:
=over 5
=item * more elaborate constructs
-=item * recursive and self-referential data structures
-
-=item * objects
-
=back
-But for now, let's look at some of the general issues common to all
-of these types of data structures.
+But for now, let's look at general issues common to all
+these types of data structures.
=head1 REFERENCES
two-dimensional one. This is actually the way almost all C
multidimensional arrays work as well.
- $list[7][12] # array of arrays
- $list[7]{string} # array of hashes
+ $array[7][12] # array of arrays
+ $array[7]{string} # array of hashes
$hash{string}[7] # hash of arrays
$hash{string}{'another string'} # hash of hashes
out your array in with a simple print() function, you'll get something
that doesn't look very nice, like this:
- @LoL = ( [2, 3], [4, 5, 7], [0] );
- print $LoL[1][2];
+ my @AoA = (
+ [2, 3, ],
+ [4, 5, 7],
+ [0, ],
+ );
+ print $AoA[1][2];
7
- print @LoL;
+ print @AoA;
ARRAY(0x83c38)ARRAY(0x8b194)ARRAY(0x8b1d0)
repeatedly. Here's the case where you just get the count instead
of a nested array:
- for $i (1..10) {
- @list = somefunc($i);
- $LoL[$i] = @list; # WRONG!
+ my @AoA;
+ for my $i (1..10) {
+ my @array = somefunc($i);
+ $AoA[$i] = @array; # WRONG!
}
-That's just the simple case of assigning a list to a scalar and getting
+That's just the simple case of assigning an array to a scalar and getting
its element count. If that's what you really and truly want, then you
might do well to consider being a tad more explicit about it, like this:
- for $i (1..10) {
- @list = somefunc($i);
- $counts[$i] = scalar @list;
- }
-
-Here's the case of taking a reference to the same memory location
-again and again:
-
- for $i (1..10) {
- @list = somefunc($i);
- $LoL[$i] = \@list; # WRONG!
+ my @counts;
+ for my $i (1..10) {
+ my @array = somefunc($i);
+ $counts[$i] = scalar @array;
}
-So, what's the big problem with that? It looks right, doesn't it?
-After all, I just told you that you need an array of references, so by
-golly, you've made me one!
-
-Unfortunately, while this is true, it's still broken. All the references
-in @LoL refer to the I<very same place>, and they will therefore all hold
-whatever was last in @list! It's similar to the problem demonstrated in
-the following C program:
+Here's the right way to do the reference C<@array>:
- #include <pwd.h>
- main() {
- struct passwd *getpwnam(), *rp, *dp;
- rp = getpwnam("root");
- dp = getpwnam("daemon");
-
- printf("daemon name is %s\nroot name is %s\n",
- dp->pw_name, rp->pw_name);
- }
-
-Which will print
-
- daemon name is daemon
- root name is daemon
-
-The problem is that both C<rp> and C<dp> are pointers to the same location
-in memory! In C, you'd have to remember to malloc() yourself some new
-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:
-
- for $i (1..10) {
- @list = somefunc($i);
- $LoL[$i] = [ @list ];
+ my @AoA
+ for my $i (1..10) {
+ my @array = somefunc($i);
+ $AoA[$i] = [ @array ];
}
The square brackets make a reference to a new array with a I<copy>
-of what's in @list at the time of the assignment. This is what
-you want.
+of what's in C<@array>.
Note that this will produce something similar, but it's
much harder to read:
- for $i (1..10) {
- @list = 0 .. $i;
- @{$LoL[$i]} = @list;
+ my @AoA;
+ for my $i (1..10) {
+ my @array = somefunc($i);
+ @{ $AoA[$i] } = @array;
}
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<@{$LoL[$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<$LoL[$i]> had been undefined to start with, or whether it
-already contained a reference. If you had already populated @LoL with
+whether C<$AoA[$i]> had been undefined to start with, or whether it
+already contained a reference. If you had already populated @AoA with
references, as in
- $LoL[3] = \@another_list;
+ $AoA[3] = \@another_array;
Then the assignment with the indirection on the left-hand-side would
use the existing reference that was already there:
- @{$LoL[3]} = @list;
+ @{ $AoA[3] } = @array;
Of course, this I<would> have the "interesting" effect of clobbering
-@another_list. (Have you ever noticed how when a programmer says
+@another_array. (Have you ever noticed how when a programmer says
something is "interesting", that rather than meaning "intriguing",
they're disturbingly more apt to mean that it's "annoying",
"difficult", or both? :-)
Surprisingly, the following dangerous-looking construct will
actually work out fine:
- for $i (1..10) {
- my @list = somefunc($i);
- $LoL[$i] = \@list;
+ my @AoA;
+ for my $i (1..10) {
+ my @array = somefunc($i);
+ $AoA[$i] = \@array;
}
That's because my() is more of a run-time statement than it is a
In summary:
- $LoL[$i] = [ @list ]; # usually best
- $LoL[$i] = \@list; # perilous; just how my() was that list?
- @{ $LoL[$i] } = @list; # way too tricky for most programmers
+ $AoA[$i] = [ @array ]; # usually best
+ $AoA[$i] = \@array; # perilous; just how my() is that array?
+ @{ $AoA[$i] } = @array; # way too tricky for most programmers
=head1 CAVEAT ON PRECEDENCE
-Speaking of things like C<@{$LoL[$i]}>, the following are actually the
+Speaking of things like C<@{ $AoA[$i] }>, the following are actually the
same thing:
- $listref->[2][2] # clear
- $$listref[2][2] # confusing
+ $aref->[2][2] # clear
+ $$aref[2][2] # confusing
That's because Perl's precedence rules on its five prefix dereferencers
(which look like someone swearing: C<$ @ * % &>) make them bind more
element of C<a>. That is, they first take the subscript, and only then
dereference the thing at that subscript. That's fine in C, but this isn't C.
-The seemingly equivalent construct in Perl, C<$$listref[$i]> first does
-the deref of C<$listref>, making it take $listref as a reference to an
+The seemingly equivalent construct in Perl, C<$$aref[$i]> first does
+the deref of $aref, making it take $aref as a reference to an
array, and then dereference that, and finally tell you the I<i'th> value
-of the array pointed to by $LoL. If you wanted the C notion, you'd have to
-write C<${$LoL[$i]}> to force the C<$LoL[$i]> to get evaluated first
+of the array pointed to by $AoA. If you wanted the C notion, you'd have to
+write C<${$AoA[$i]}> to force the C<$AoA[$i]> to get evaluated first
before the leading C<$> dereferencer.
=head1 WHY YOU SHOULD ALWAYS C<use strict>
also disallow accidental "symbolic dereferencing". Therefore if you'd done
this:
- my $listref = [
- [ "fred", "barney", "pebbles", "bambam", "dino", ],
- [ "homer", "bart", "marge", "maggie", ],
- [ "george", "jane", "elroy", "judy", ],
+ my $aref = [
+ [ 'fred', 'barney', 'pebbles', 'bambam', 'dino', ],
+ [ 'homer', 'bart', 'marge', 'maggie', ],
+ [ 'george', 'jane', 'elroy', 'judy', ],
];
- print $listref[2][2];
+ print $aref[2][2];
The compiler would immediately flag that as an error I<at compile time>,
-because you were accidentally accessing C<@listref>, an undeclared
+because you were accidentally accessing C<@aref>, an undeclared
variable, and it would thereby remind you to write instead:
- print $listref->[2][2]
+ print $aref->[2][2]
=head1 DEBUGGING
printing out complex data structures. With 5.002 or above, the
debugger includes several new features, including command line editing as
well as the C<x> command to dump out complex data structures. For
-example, given the assignment to $LoL above, here's the debugger output:
+example, given the assignment to $AoA above, here's the debugger output:
- DB<1> X $LoL
- $LoL = ARRAY(0x13b5a0)
+ DB<1> x $AoA
+ $AoA = ARRAY(0x13b5a0)
0 ARRAY(0x1f0a24)
0 'fred'
1 'barney'
2 'elroy'
3 'judy'
-There's also a lower-case B<x> command which is nearly the same.
-
=head1 CODE EXAMPLES
-Presented with little comment (these will get their own man pages someday)
+Presented with little comment (these will get their own manpages someday)
here are short code examples illustrating access of various
types of data structures.
-=head1 LISTS OF LISTS
+=head1 ARRAYS OF ARRAYS
-=head2 Declaration of a LIST OF LISTS
+=head2 Declaration of a ARRAY OF ARRAYS
- @LoL = (
- [ "fred", "barney" ],
- [ "george", "jane", "elroy" ],
- [ "homer", "marge", "bart" ],
+ my @AoA = (
+ [ 'fred', 'barney' ],
+ [ 'george', 'jane', 'elroy' ],
+ [ 'homer', 'marge', 'bart' ],
);
-=head2 Generation of a LIST OF LISTS
+=head2 Generation of a ARRAY OF ARRAYS
# reading from file
+ my @AoA;
while ( <> ) {
- push @LoL, [ split ];
+ push @AoA, [ split ];
}
# calling a function
- for $i ( 1 .. 10 ) {
- $LoL[$i] = [ somefunc($i) ];
+ my @AoA;
+ foreach my $i ( 1 .. 10 ) {
+ $AoA[$i] = [ somefunc($i) ];
}
# using temp vars
- for $i ( 1 .. 10 ) {
- @tmp = somefunc($i);
- $LoL[$i] = [ @tmp ];
+ my @AoA;
+ foreach my $i ( 1 .. 10 ) {
+ my @tmp = somefunc($i);
+ $AoA[$i] = [ @tmp ];
}
# add to an existing row
- push @{ $LoL[0] }, "wilma", "betty";
+ push @{ $AoA[0] }, 'wilma', 'betty';
+
+=head2 Access and Printing of a ARRAY OF ARRAYS
-=head2 Access and Printing of a LIST OF LISTS
+ my @AoA;
# one element
- $LoL[0][0] = "Fred";
+ $AoA[0][0] = 'Fred';
# another element
- $LoL[1][1] =~ s/(\w)/\u$1/;
+ $AoA[1][1] =~ s/(\w)/\u$1/;
# print the whole thing with refs
- for $aref ( @LoL ) {
+ foreach my $aref ( @AoA ) {
print "\t [ @$aref ],\n";
}
# print the whole thing with indices
- for $i ( 0 .. $#LoL ) {
- print "\t [ @{$LoL[$i]} ],\n";
+ foreach my $i ( 0 .. $#AoA ) {
+ print "\t [ @{ $AoA[$i] } ],\n";
}
# print the whole thing one at a time
- for $i ( 0 .. $#LoL ) {
- for $j ( 0 .. $#{$LoL[$i]} ) {
- print "elt $i $j is $LoL[$i][$j]\n";
+ foreach my $i ( 0 .. $#AoA ) {
+ foreach my $j ( 0 .. $#{ $AoA[$i] } ) {
+ print "element $i $j is $AoA[$i][$j]\n";
}
}
-=head1 HASHES OF LISTS
+=head1 HASHES OF ARRAYS
-=head2 Declaration of a HASH OF LISTS
+=head2 Declaration of a HASH OF ARRAYS
- %HoL = (
- "flintstones" => [ "fred", "barney" ],
- "jetsons" => [ "george", "jane", "elroy" ],
- "simpsons" => [ "homer", "marge", "bart" ],
+ my %HoA = (
+ flintstones => [ 'fred', 'barney' ],
+ jetsons => [ 'george', 'jane', 'elroy' ],
+ simpsons => [ 'homer', 'marge', 'bart' ],
);
-=head2 Generation of a HASH OF LISTS
+=head2 Generation of a HASH OF ARRAYS
# reading from file
# flintstones: fred barney wilma dino
+ my %HoA;
while ( <> ) {
- next unless s/^(.*?):\s*//;
- $HoL{$1} = [ split ];
+ next unless s/^([^:]*):\s*//;
+ $HoA{$1} = [ split ];
}
# reading from file; more temps
# flintstones: fred barney wilma dino
- while ( $line = <> ) {
- ($who, $rest) = split /:\s*/, $line, 2;
- @fields = split ' ', $rest;
- $HoL{$who} = [ @fields ];
+ my %HoA;
+ while ( my $line = <> ) {
+ my ($who, $rest) = split /:\s*/, $line, 2;
+ my @fields = split ' ', $rest;
+ $HoA{$who} = [ @fields ];
}
# calling a function that returns a list
- for $group ( "simpsons", "jetsons", "flintstones" ) {
- $HoL{$group} = [ get_family($group) ];
+ my %HoA;
+ foreach my $group ( 'simpsons', 'jetsons', 'flintstones' ) {
+ $HoA{$group} = [ get_family($group) ];
}
# likewise, but using temps
- for $group ( "simpsons", "jetsons", "flintstones" ) {
- @members = get_family($group);
- $HoL{$group} = [ @members ];
+ my %HoA;
+ foreach my $group ( 'simpsons', 'jetsons', 'flintstones' ) {
+ my @members = get_family($group);
+ $HoA{$group} = [ @members ];
}
# append new members to an existing family
- push @{ $HoL{"flintstones"} }, "wilma", "betty";
+ push @{ $HoA{flintstones} }, 'wilma', 'betty';
+
+=head2 Access and Printing of a HASH OF ARRAYS
-=head2 Access and Printing of a HASH OF LISTS
+ my %HoA;
# one element
- $HoL{flintstones}[0] = "Fred";
+ $HoA{flintstones}[0] = 'Fred';
# another element
- $HoL{simpsons}[1] =~ s/(\w)/\u$1/;
+ $HoA{simpsons}[1] =~ s/(\w)/\u$1/;
# print the whole thing
- foreach $family ( keys %HoL ) {
- print "$family: @{ $HoL{$family} }\n"
+ foreach my $family ( keys %HoA ) {
+ print "$family: @{ $HoA{$family} }\n";
}
# print the whole thing with indices
- foreach $family ( keys %HoL ) {
- print "family: ";
- foreach $i ( 0 .. $#{ $HoL{$family} } ) {
- print " $i = $HoL{$family}[$i]";
+ foreach my $family ( keys %HoA ) {
+ print 'family: ';
+ foreach my $i ( 0 .. $#{ $HoA{$family} } ) {
+ print " $i = $HoA{$family}[$i]";
}
print "\n";
}
# print the whole thing sorted by number of members
- foreach $family ( sort { @{$HoL{$b}} <=> @{$HoL{$b}} } keys %HoL ) {
- print "$family: @{ $HoL{$family} }\n"
+ sub num_members {
+ @{ $HoA{$b} } <=> @{ $HoA{$a} }
+ }
+ foreach my $family ( sort num_members keys %HoA ) {
+ print "$family: @{ $HoA{$family} }\n"
}
# print the whole thing sorted by number of members and name
- foreach $family ( sort { @{$HoL{$b}} <=> @{$HoL{$a}} } keys %HoL ) {
- print "$family: ", join(", ", sort @{ $HoL{$family}), "\n";
+ sub members_and_name {
+ @{ $HoA{$b} } <=> @{ $HoA{$a} }
+ ||
+ $a cmp $b
+ }
+ foreach my $family ( sort members_and_name keys %HoA ) {
+ print "$family: ", join(", ", sort @{ $HoA{$family} }), "\n";
}
-=head1 LISTS OF HASHES
+=head1 ARRAYS OF HASHES
-=head2 Declaration of a LIST OF HASHES
+=head2 Declaration of a ARRAY OF HASHES
- @LoH = (
+ my @AoH = (
{
- Lead => "fred",
- Friend => "barney",
+ Lead => 'fred',
+ Friend => 'barney',
},
{
- Lead => "george",
- Wife => "jane",
- Son => "elroy",
+ Lead => 'george',
+ Wife => 'jane',
+ Son => 'elroy',
},
{
- Lead => "homer",
- Wife => "marge",
- Son => "bart",
+ Lead => 'homer',
+ Wife => 'marge',
+ Son => 'bart',
}
);
-=head2 Generation of a LIST OF HASHES
+=head2 Generation of a ARRAY OF HASHES
# reading from file
# format: LEAD=fred FRIEND=barney
+ my @AoH;
while ( <> ) {
- $rec = {};
- for $field ( split ) {
- ($key, $value) = split /=/, $field;
- $rec->{$key} = $value;
+ my $rec = {};
+ foreach my $field ( split ) {
+ my($key, $value) = split /=/, $field;
+ $rec->{$key} = $value;
}
- push @LoH, $rec;
+ push @AoH, $rec;
}
# reading from file
# format: LEAD=fred FRIEND=barney
# no temp
+ my @AoH;
while ( <> ) {
- push @LoH, { split /[\s+=]/ };
+ push @AoH, { split /[\s+=]/ };
}
- # calling a function that returns a key,value list, like
- # "lead","fred","daughter","pebbles"
- while ( %fields = getnextpairset() ) {
- push @LoH, { %fields };
+ # calling a function that returns a key/value pair list, like
+ # lead => 'fred', daughter => 'pebbles'
+ my @AoH;
+ while ( my %fields = getnextpairset() ) {
+ push @AoH, { %fields };
}
# likewise, but using no temp vars
+ my @AoH;
while (<>) {
- push @LoH, { parsepairs($_) };
+ push @AoH, { parsepairs($_) };
}
# add key/value to an element
- $LoH[0]{pet} = "dino";
- $LoH[2]{pet} = "santa's little helper";
+ $AoH[0]{pet} = 'dino';
+ $AoH[2]{pet} = "santa's little helper";
-=head2 Access and Printing of a LIST OF HASHES
+=head2 Access and Printing of a ARRAY OF HASHES
+
+ my @AoH;
# one element
- $LoH[0]{lead} = "fred";
+ $AoH[0]{lead} = 'fred';
# another element
- $LoH[1]{lead} =~ s/(\w)/\u$1/;
+ $AoH[1]{lead} =~ s/(\w)/\u$1/;
# print the whole thing with refs
- for $href ( @LoH ) {
- print "{ ";
- for $role ( keys %$href ) {
- print "$role=$href->{$role} ";
+ foreach my $href ( @AoH ) {
+ print '{ ';
+ foreach my $role ( keys %$href ) {
+ print "$role = $href->{$role} ";
}
print "}\n";
}
# print the whole thing with indices
- for $i ( 0 .. $#LoH ) {
+ foreach my $i ( 0 .. $#AoH ) {
print "$i is { ";
- for $role ( keys %{ $LoH[$i] } ) {
- print "$role=$LoH[$i]{$role} ";
+ foreach my $role ( keys %{ $AoH[$i] } ) {
+ print "$role = $AoH[$i]{$role} ";
}
print "}\n";
}
# print the whole thing one at a time
- for $i ( 0 .. $#LoH ) {
- for $role ( keys %{ $LoH[$i] } ) {
- print "elt $i $role is $LoH[$i]{$role}\n";
+ foreach my $i ( 0 .. $#AoH ) {
+ foreach my $role ( keys %{ $AoH[$i] } ) {
+ print "element $i $role is $AoH[$i]{$role}\n";
}
}
=head2 Declaration of a HASH OF HASHES
- %HoH = (
- "flintstones" => {
- "lead" => "fred",
- "pal" => "barney",
+ my %HoH = (
+ flintstones => {
+ lead => 'fred',
+ pal => 'barney',
},
- "jetsons" => {
- "lead" => "george",
- "wife" => "jane",
- "his boy" => "elroy",
+ jetsons => {
+ lead => 'george',
+ wife => 'jane',
+ 'his boy' => 'elroy',
},
- "simpsons" => {
- "lead" => "homer",
- "wife" => "marge",
- "kid" => "bart",
+ simpsons => {
+ lead => 'homer',
+ wife => 'marge',
+ kid => 'bart',
},
);
# reading from file
# flintstones: lead=fred pal=barney wife=wilma pet=dino
+ my %HoH;
while ( <> ) {
- next unless s/^(.*?):\s*//;
- $who = $1;
- for $field ( split ) {
- ($key, $value) = split /=/, $field;
+ next unless s/^([^:]*):\s*//;
+ my $who = $1;
+ for my $field ( split ) {
+ my($key, $value) = split /=/, $field;
$HoH{$who}{$key} = $value;
}
# reading from file; more temps
+ my %HoH;
while ( <> ) {
- next unless s/^(.*?):\s*//;
- $who = $1;
- $rec = {};
+ next unless s/^([^:]*):\s*//;
+ my $who = $1;
+ my $rec = {};
$HoH{$who} = $rec;
- for $field ( split ) {
- ($key, $value) = split /=/, $field;
- $rec->{$key} = $value;
+ foreach my $field ( split ) {
+ my($key, $value) = split /=/, $field;
+ $rec->{$key} = $value;
}
}
# calling a function that returns a key,value hash
- for $group ( "simpsons", "jetsons", "flintstones" ) {
+ my %HoH;
+ foreach my $group ( 'simpsons', 'jetsons', 'flintstones' ) {
$HoH{$group} = { get_family($group) };
}
# likewise, but using temps
- for $group ( "simpsons", "jetsons", "flintstones" ) {
- %members = get_family($group);
+ my %HoH;
+ foreach my $group ( 'simpsons', 'jetsons', 'flintstones' ) {
+ my %members = get_family($group);
$HoH{$group} = { %members };
}
# append new members to an existing family
- %new_folks = (
- "wife" => "wilma",
- "pet" => "dino";
+ my %HoH;
+ my %new_folks = (
+ wife => 'wilma',
+ pet => 'dino',
);
- for $what (keys %new_folks) {
+ foreach my $what (keys %new_folks) {
$HoH{flintstones}{$what} = $new_folks{$what};
}
=head2 Access and Printing of a HASH OF HASHES
+ %HoH;
+
# one element
- $HoH{flintstones}{wife} = "wilma";
+ $HoH{flintstones}{wife} = 'wilma';
# another element
$HoH{simpsons}{lead} =~ s/(\w)/\u$1/;
# print the whole thing
- foreach $family ( keys %HoH ) {
+ foreach my $family ( keys %HoH ) {
print "$family: { ";
- for $role ( keys %{ $HoH{$family} } ) {
- print "$role=$HoH{$family}{$role} ";
+ foreach my $role ( keys %{ $HoH{$family} } ) {
+ print "$role = $HoH{$family}{$role} ";
}
print "}\n";
}
# print the whole thing somewhat sorted
- foreach $family ( sort keys %HoH ) {
+ foreach my $family ( sort keys %HoH ) {
print "$family: { ";
- for $role ( sort keys %{ $HoH{$family} } ) {
- print "$role=$HoH{$family}{$role} ";
+ foreach my $role ( sort keys %{ $HoH{$family} } ) {
+ print "$role = $HoH{$family}{$role} ";
}
print "}\n";
}
-
# print the whole thing sorted by number of members
- foreach $family ( sort { keys %{$HoH{$b}} <=> keys %{$HoH{$b}} } keys %HoH ) {
+ sub num_members {
+ keys %{ $HoH{$b} } <=> keys %{ $HoH{$a} }
+ }
+ foreach my $family ( sort num_members keys %HoH ) {
print "$family: { ";
- for $role ( sort keys %{ $HoH{$family} } ) {
- print "$role=$HoH{$family}{$role} ";
+ foreach my $role ( sort keys %{ $HoH{$family} } ) {
+ print "$role = $HoH{$family}{$role} ";
}
print "}\n";
}
# establish a sort order (rank) for each role
- $i = 0;
- for ( qw(lead wife son daughter pal pet) ) { $rank{$_} = ++$i }
+ my %rank;
+ my $i = 0;
+ foreach ( qw(lead wife son daughter pal pet) ) {
+ $rank{$_} = ++$i;
+ }
# now print the whole thing sorted by number of members
- foreach $family ( sort { keys %{$HoH{$b}} <=> keys %{$HoH{$b}} } keys %HoH ) {
+ sub num_members {
+ keys %{ $HoH{$b} } <=> keys %{ $HoH{$a} }
+ }
+ sub rank {
+ $rank{$a} <=> $rank{$b}
+ }
+
+ foreach my $family ( sort num_members keys %HoH ) {
print "$family: { ";
# and print these according to rank order
- for $role ( sort { $rank{$a} <=> $rank{$b} keys %{ $HoH{$family} } } ) {
- print "$role=$HoH{$family}{$role} ";
+ foreach my $role ( sort rank keys %{ $HoH{$family} } ) {
+ print "$role = $HoH{$family}{$role} ";
}
print "}\n";
}
Here's a sample showing how to create and use a record whose fields are of
many different sorts:
- $rec = {
+ my $rec = {
TEXT => $string,
SEQUENCE => [ @old_values ],
LOOKUP => { %some_table },
print $rec->{TEXT};
- print $rec->{LIST}[0];
- $last = pop @ { $rec->{SEQUENCE} };
+ print $rec->{SEQUENCE}->[0];
+ my $last = pop @{ $rec->{SEQUENCE} };
- print $rec->{LOOKUP}{"key"};
- ($first_k, $first_v) = each %{ $rec->{LOOKUP} };
+ print $rec->{LOOKUP}->{key};
+ my($first_k, $first_v) = each %{ $rec->{LOOKUP} };
- $answer = &{ $rec->{THATCODE} }($arg);
- $answer = &{ $rec->{THISCODE} }($arg1, $arg2);
+ my $answer = $rec->{THATCODE}->($arg);
+ my $result = $rec->{THISCODE}->($arg1, $arg2);
# careful of extra block braces on fh ref
print { $rec->{HANDLE} } "a string\n";
=head2 Declaration of a HASH OF COMPLEX RECORDS
- %TV = (
- "flintstones" => {
- series => "flintstones",
+ my %TV = (
+ flintstones => {
+ series => 'flintstones',
nights => [ qw(monday thursday friday) ],
members => [
- { name => "fred", role => "lead", age => 36, },
- { name => "wilma", role => "wife", age => 31, },
- { name => "pebbles", role => "kid", age => 4, },
+ { name => 'fred', role => 'lead', age => 36, },
+ { name => 'wilma', role => 'wife', age => 31, },
+ { name => 'pebbles', role => 'kid', age => 4, },
],
},
- "jetsons" => {
- series => "jetsons",
+ jetsons => {
+ series => 'jetsons',
nights => [ qw(wednesday saturday) ],
members => [
- { name => "george", role => "lead", age => 41, },
- { name => "jane", role => "wife", age => 39, },
- { name => "elroy", role => "kid", age => 9, },
+ { name => 'george", role => 'lead', age => 41, },
+ { name => 'jane", role => 'wife', age => 39, },
+ { name => 'elroy", role => 'kid', age => 9, },
],
},
- "simpsons" => {
- series => "simpsons",
+ simpsons => {
+ series => 'simpsons',
nights => [ qw(monday) ],
members => [
- { name => "homer", role => "lead", age => 34, },
- { name => "marge", role => "wife", age => 37, },
- { name => "bart", role => "kid", age => 11, },
+ { name => 'homer', role => 'lead', age => 34, },
+ { name => 'marge', role => 'wife', age => 37, },
+ { name => 'bart', role => 'kid', age => 11, },
],
},
);
=head2 Generation of a HASH OF COMPLEX RECORDS
- # reading from file
- # this is most easily done by having the file itself be
- # in the raw data format as shown above. perl is happy
- # to parse complex data structures if declared as data, so
- # sometimes it's easiest to do that
+Here's a piece by piece build up of a hash of complex records. We'll
+read in a file that has our data in it.
- # here's a piece by piece build up
- $rec = {};
- $rec->{series} = "flintstones";
+ my %TV = ();
+ my $rec = {};
+ $rec->{series} = 'flintstones';
$rec->{nights} = [ find_days() ];
- @members = ();
+ my @members = ();
# assume this file in field=value syntax
- while (<>) {
- %fields = split /[\s=]+/;
+ while ( <> ) {
+ my %fields = split /[\s=]+/, $_;
push @members, { %fields };
}
$rec->{members} = [ @members ];
# now remember the whole thing
$TV{ $rec->{series} } = $rec;
- ###########################################################
- # now, you might want to make interesting extra fields that
- # include pointers back into the same data structure so if
- # change one piece, it changes everywhere, like for examples
- # if you wanted a {kids} field that was an array reference
- # to a list of the kids' records without having duplicate
- # records and thus update problems.
- ###########################################################
- foreach $family (keys %TV) {
- $rec = $TV{$family}; # temp pointer
- @kids = ();
- for $person ( @{$rec->{members}} ) {
- if ($person->{role} =~ /kid|son|daughter/) {
+Now, you might want to make interesting extra fields that
+include pointers back into the same data structure so if
+change one piece, it changes everywhere, like for example
+if you wanted a 'kids' field that was a reference
+to an array of the kids' records without having duplicate
+records and thus update problems.
+
+ foreach my $family ( keys %TV ) {
+ my $rec = $TV{$family}; # $rec points to $TV{$family}
+ my @kids = ();
+ foreach my $person ( @{ $rec->{members} } ) {
+ if ( $person->{role} =~ /kid|son|daughter/ ) {
push @kids, $person;
}
}
$rec->{kids} = [ @kids ];
}
- # you copied the list, but the list itself contains pointers
- # to uncopied objects. this means that if you make bart get
- # older via
+You copied the array, but the array itself contains pointers
+to uncopied objects. This means that if you make bart get
+older via
$TV{simpsons}{kids}[0]{age}++;
- # then this would also change in
- print $TV{simpsons}{members}[2]{age};
-
- # because $TV{simpsons}{kids}[0] and $TV{simpsons}{members}[2]
- # both point to the same underlying anonymous hash table
+Then this would also change in C<$TV{simpsons}{members}[2]{age}>
+because C<$TV{simpsons}{kids}[0]> and C<$TV{simpsons}{members}[2]>
+both point to the same underlying anonymous hash table.
# print the whole thing
- foreach $family ( keys %TV ) {
- print "the $family";
- print " is on during @{ $TV{$family}{nights} }\n";
- print "its members are:\n";
- for $who ( @{ $TV{$family}{members} } ) {
+ foreach my $family ( keys %TV ) {
+ print "the $family is on during @{ $TV{$family}{nights} }\n",
+ "its members are:\n";
+
+ foraech my $who ( @{ $TV{$family}{members} } ) {
print " $who->{name} ($who->{role}), age $who->{age}\n";
}
- print "it turns out that $TV{$family}{'lead'} has ";
- print scalar ( @{ $TV{$family}{kids} } ), " kids named ";
- print join (", ", map { $_->{name} } @{ $TV{$family}{kids} } );
- print "\n";
+
+ print "it turns out that $TV{$family}{lead} has ",
+ scalar ( @{ $TV{$family}{kids} } ),
+ ' kids named ',
+ join(
+ ', ',
+ map { $_->{name} } @{ $TV{$family}{kids} }
+ ),
+ "\n";
}
=head1 Database Ties
Berkeley DB have size limitations, but beyond that, you also have problems
with how references are to be represented on disk. One experimental
module that does partially attempt to address this need is the MLDBM
-module. Check your nearest CPAN site as described in L<perlmod> for
+module. Check your nearest CPAN site as described in L<perlmodlib> for
source code to MLDBM.
=head1 SEE ALSO
=head1 AUTHOR
-Tom Christiansen E<lt>F<tchrist@perl.com>E<gt>
+Tom Christiansen <F<tchrist@perl.com>>
+
+Last update (by Tom):
+Wed Oct 23 04:57:50 MET DST 1996
-Last update:
-Mon Jul 8 05:22:49 MDT 1996
+Last update (by Casey West, <F<casey@geeknest.com>>
+Mon Sep 17 13:33:41 EDT 2001
projects / p5sagit/p5-mst-13.2.git / blobdiff