Identifying positions of the last TRUEs in a sequence of TRUEs and FALSEs

Taking advantage of diff with an appended FALSE to catch the implied TRUE-to-FALSE at the end.

diff(c(x,FALSE)) == -1
# [1] FALSE FALSE FALSE FALSE FALSE  TRUE FALSE FALSE FALSE FALSE FALSE  TRUE
#[13] FALSE FALSE  TRUE

We may look where x is greater than shifted x with 0 appended.

x>c(x[-1],0)
# [1] FALSE FALSE FALSE FALSE FALSE  TRUE FALSE FALSE FALSE FALSE FALSE  TRUE FALSE FALSE  TRUE