data.frame to array?

I do not think that the form [[1:3]] is legit.

sure it is.

ltest <- list( "a", "b", "c", "d")
ltest[[1:3]]

Error in ltest[[1:3]] : recursive indexing failed at level 2

read the error message:  *recursive* indexing failed.  that's because
ltest[[1]] has only one element while you wanted its second element (and
that element's third element).

    ltest = list(list(2, as.list(1:3)))
    ltest[[1:3]]
    # 3

is just fine.

vQ