Where are the docs for the DataFrames by() function

General Usage
1

I can’t find any docs for the by() function in DataFrames. There is an example of usage here, but no docs:

http://dataframesjl.readthedocs.io/en/latest/reshaping_and_pivoting.html?highlight=by

2

At the REPL, ?by works for me.

3

I guess the REPL is the only documentation. The REPL showed this which was helpful:

by(d, cols, f) is equivalent to combine(map(f, groupby(d, cols)))

4

Found this while searching for the DataFrames.nrow function:

https://en.wikibooks.org/wiki/Introducing_Julia/DataFrames