Split Data Frame into Rows of Fixed Size

Split Data Frame into Rows of Fixed Size

I have a bunch of data frames with varying degrees of length, ranging from
approx. 15,000 to 500,000. For each of these data frames, I would like to
split them up into smaller data frames each with 300 rows which I would do
further processing on. How can I do this?
This (Split up a dataframe in R by number of rows) provides a partial
answer, but it doesn't work because not all my data frames have length
that are multiples of 300.
Would greatly appreciate it if a plyr and non-plyr solution can both be
provided.
Thank you!