f355.3 <- function(x, y)
{
STR.SPLIT <- strsplit(x," ")[[1]]

## y = c(3, 5, 1) で c(1,1,1,2,2,2,2,2,3)を返す
GROUP <- inverse.rle(list(lengths = y,
values = seq_along(y)))

## 上記のGROUPにあわせてsplit()
split(x = STR.SPLIT[seq_along(GROUP)], f = GROUP)
}

## これなら数字の順番がめちゃくちゃでも、文字列でも行けるかも。spaceが続くとおかしくなるけど
f355.3(x = "2 ch R 2012 01 26 2 0 1 2 0 1 2 6 R", y = c(3, 5, 1, 2, 2))