Best way to store variable-length data in an R data.frame?

Question

I have some mixed-type data that I would like to store in an R data structure of some sort. Each data point has a set of fixed attributes which may be 1-d numeric, factors, or

Answer 1

I would also use strings for the variable length data, but as in the following example: "c(5,5)" for the first phrase. One needs to use eval(parse(text=...)) to carry out computations.

For example, the mean can be computed as follows:

sapply(data$token_lengths,function(str) mean(eval(parse(text=str))))