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### Re^3: How to create a two dimensional queue in Perl

by pemungkah (Priest)
 on Aug 05, 2013 at 02:15 UTC ( #1047846=note: print w/replies, xml ) Need Help??

I'm assuming that these aren't priority queues - just items in whatever order they've been added into the queues. So here's how to go about it.
```# Start with an empty master queue.
my @master;

# Build a sub queue. Note that this is a array *reference*.
my \$subqueue = [ 1, 2, 3, 4];

# add it to the queue. push() puts it at the tail of the queue.
push @master, \$subqueue;

# Now let's create a couple more sub queues and add them.
push @master, [5, 6, 7];

# Some high-priority-items we'll stick at the front of the master:
unshift @master, [-1, 0];

# Now let's run the queue. We look at the master. If there are no item
+s remaining,
# the queue is empty. Otherwise, process the leading sub queue.
while (@master) {
# If the leading sub queue is empty, discard it, and start over with
+ the rest of
# the (now possibly empty) master queue.
while  ( @{ \$master[0] } ) {
my \$item = shift @{ \$master[0] };
print \$item, " ";
}
# We arrive here when the sub queue is empty. Discard the empty sub
+queue.
shift @master;
# Move to the next line so we can see we switched sub queues.
print "\n"
}
print "\n";
The output will be
```-1 0
1 2 3 4
5 6 7
Obviously this is a toy program, but it serves to demonstrate the basic array operations and tests that are needed to manage a queue of queues. More complex operations (like priority queuing, etc.) are left as an exercise. (I'd probably switch the plain scalar values for anonymous hashes, one item of which is a 'priority' field that you can sort the array of hashes on, and the other a 'value' which will be either the scalar value you want in the node (on the sub queues) or a reference to a subqueue (for the master).)

And of course this isn't a class; that'd be a nice thing to do as well.

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