Hmm, I don't understand exactly what is is that you don't understand :-). The design of n f\ y came about as follows. The concept of "moving window" is well-known (moving average, moving maximum, etc.). When n is a positive integer, the interpretation is "obvious":
4 <\ 'abcdefg' ┌────┬────┬────┬────┐ │abcd│bcde│cdef│defg│ └────┴────┴────┴────┘ 3 <\ 'abcdefg' ┌───┬───┬───┬───┬───┐ │abc│bcd│cde│def│efg│ └───┴───┴───┴───┴───┘ In n f\y, the function f is applied to each window of size n. The windows overlap and move by 1 each time. When n is a negative integer, the definition is that the windows are of size -n and do not overlap. One of the anticipated uses is exactly the one you need, where you have a vector and you want to make it into a matrix with -n columns. _4 <\ 'abcdefg' ┌────┬───┐ │abcd│efg│ └────┴───┘ _3 <\ 'abcdefg' ┌───┬───┬─┐ │abc│def│g│ └───┴───┴─┘ _4 ]\ 'abcdefg' abcd efg _3 ]\ 'abcdefg' abc def g On Tue, Oct 9, 2012 at 5:46 AM, Dr. Heinz Schild < [email protected]> wrote: > Thank you for the very elegant formulation. > However, why "_2" works as it does, I do not understand. > > > Am 08.10.2012 um 20:10 schrieb Roger Hui <[email protected]>: > > > _2 ]\ 0".jfromcb '' may work, depending on your views on how an odd > > number of input numbers should be handled. > > > > > > > > On Mon, Oct 8, 2012 at 11:00 AM, Dr. Heinz Schild > > <[email protected]> wrote: > >> I want to read a list with coordinates (x, y) of unknown length from > the clipboard into an iPad and transform it into a table with 2 columns. > The following line works: > >> ((<.-:# Zi),2)$ Zi=. 0". jfromcb '' > >> But is there a better way using only a tacit formulation? > >> Heinz > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
