Here's a way:
#!/usr/local/bin/perl
use strict;
use warnings;
my %hash = (
'a' => {
'x' => 40,
'z' => 102
},
'b' => {
'z' => 100,
'x' => 10,
'y' => 20
},
'c' => {
'x' => 50
},
'd' => {
'z' => 101,
'y' => 30
}
);
my $x_but_not_y = 0;
my $z = 0;
foreach my $key (keys %hash) {
$x_but_not_y++ if defined $hash{$key}->{x} and not defined $hash{$
+key}->{y};
$z++ if defined $hash{$key}->{z};
}
print "number of keys where x defined, but not y: $x_but_not_y\n";
print "number of keys where z defined: $z\n";
Arjen