Convert a "by" object to a data frame in R

The by function returns a list, so you can do something like this:

data.frame(do.call("rbind", by(x, column, mean)))

Old thread, but for anyone who searches for this topic:

analysis = by(...)
data.frame(t(vapply(analysis,unlist,unlist(analysis[[1]]))))

unlist() will take an element of a by() output (in this case, analysis) and express it as a named vector. vapply() does unlist to all the elemnts of analysis and outputs the result. It requires a dummy argument to know the output type, which is what analysis[[1]] is there for. You may need to add a check that analysis is not empty if that will be possible. Each output will be a column, so t() transposes it to the desired orientation where each analysis entry becomes a row.

Consider using ddply in the plyr package instead of by. It handles the work of adding the column to your dataframe.