问题
I have a data frame with 100 entries, and I want to get a fields value for a subset of the entries. Specifically, I want every other 10 entries (i.e. indices 1-10,21-30,41-50,61-70,...)
The only way I've been able to do this is via: c(data$field[1:10],data$field[21:30],...)
But this seems like a horrible solution, especially if the size of the data frame changes.
回答1:
You can do
data$field[rep(c(TRUE, FALSE), each = 10)]
whererep creates a vector of ten TRUE followed by ten FALSE and is recycled as needed when used for indexing.
来源：https://stackoverflow.com/questions/14794602/selecting-multiple-parts-of-a-list