Number of connections in a hash of arrays - arrays

Question

I have a hash of arrays like the following:
my %HoA = (
"M" => [ "L", "E" ],
"L" => [ "I" ],
"E" => [ "B", "C" ],
"B" => [ "A" ],
"C" => [ "A" ]
);
You can visualize it in this way:
M
/ \
L E
/ / \
I B C
\ /
A
Now, I would like to know the number of connections for every node:
M 6
E 3
L 1
B 1
C 1
I 0
A 0
With the igraph package in R this is straightforward but I am struggling to do the same with a hash of arrays in Perl.

Answer 1

You can build graphs in Perl using the Graph module
You need a Graph::Directed object
Here's an example
use strict;
use warnings 'all';
use Graph::Directed;
my %HoA = (
"M" => [ "L", "E" ],
"L" => [ "I" ],
"E" => [ "B", "C" ],
"B" => [ "A" ],
"C" => [ "A" ]
);
# Build the graph
#
my $g = Graph::Directed->new;
while ( my ($from, $to) = each %HoA ) {
$g->add_edge($from, $_) for #$to;
}
# Build a table of successors of each vertex
#
my %succ;
for my $v ( $g->vertices ) {
my #succ = $g->all_successors($v);
$succ{$v} = \#succ;
}
# Print the vertices in descending order of successors
#
for my $v ( sort { #{$succ{$b}} <=> #{$succ{$a}} } $g->vertices ) {
printf "%s %d\n", $v, scalar #{$succ{$v}};
}
output
M 6
E 3
C 1
B 1
L 1
A 0
I 0