Question

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.

Answer 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.