hadley/productplots — pull request #4 by ppham27 (2012-08-31 18:15:39+00:00)
Title: I'm not sure if this behavior is intentional or not, but prodplot(happy, ~ happy, 'tile') does not work because two rectangles had the same left boundary and ddply was only splitting by left boundaries in col_labels.

prodplot(happy, ~ happy, 'tile')
did not work due to two groups having the same left boundary and ddply was only splitting by left boundaries in col_labels.