The current freqItems API is really awkward to use. It returns a DataFrame with a single row, in which each value is an array of frequent items.
This design doesn't work well for exploratory data analysis (running show – when there are more than 2 or 3 frequent values, the values get cut off):
It also doesn't work well for serious engineering, since it is hard to get the value out.
We should create a new function (so we maintain source/binary compatibility) that returns a list of list of values.