Tool for viewing top N items in stream

I'm looking for an existing Linux command-line tools that can accomplish the following: Consider there is an input stream /dev/inputstream which spews an infinite stream of data that looks like this: A A B A C Z A . . . **NOTE:** (Each line is one character from the alphabet). The tool is used in the following fashion: cat /dev/inputstream | tool The output of the tool should be like the one from "top" command. It should be a continuously updated list of top N frequently occurring items. Eg: A -- 10 times B -- 8 times Z -- 7 times C -- 2 times D -- 1 time If the stream were not infinite I could have accomplished this using sort and uniq.