Solution is complex but works. A better solution should be pursued.
While researching a better solution the following example solution was
found: http://en.wikibooks.org/wiki/Clojure_Programming/By_Example. The
key points in this solution is using the reduce function to create a
single map from each map for each word. The second point is using the
default of 0 if a key does not already exist in the map.