Expand ranges defined by “from” and “to” columns

Question

I have a data frame containing \"name\" of U.S. Presidents, the years when they start and end in office, (\"from\" and \"to\" columns

Answer 1

Use by to create a by list L of data.frames, one data.frame per president, and then rbind them together. No packages are used.

L <- by(presidents, presidents$name, with, data.frame(name, year = from:to))
do.call("rbind", setNames(L, NULL))

If you don't mind row names then the last line could be reduced to just:

do.call("rbind", L)