R/groups.R

In vlulla/vlutils: Common utilities that I find useful

groups <-
function(vector, numitems, overlapping=FALSE) {
  ## Emulates the following J idioms
  ##
  ##     3 ]\ i.10
  ##    _3 ]\ i.10
  ##
  ## Try the following in your R console:
  ##
  ##    R> l <- 1:15
  ##    R> groups(l, 3)                    ## Same as _3 ]\ i.15
  ##    R> groups(l, 3, overlapping=TRUE)  ## Same as  3 ]\ i.15

  startidx <- if (overlapping) {
    1:(length(vector) - numitems + 1)
  } else {
    seq(1, length(vector), by=numitems)
  }
  endidx <- startidx + numitems - 1
  t(mapply(function(x,y) vector[x:y], startidx, endidx))
}