pair2=:([:;],."0 _&.>[:<\.1&+)@i.@<: (pair2-:pairi) 100 1
=@@i Matthew Brand schreef: > Hi All, > > I came up with this program to generate pairs of indices to select all > unique pairs from a list. Is there a built in J way to do this? I > looked at C. and A. but could not see how to achieve the below. > > Thanks, > Matthew. > > > pairi =: ( ( ] #~ [: (~:/)"1 ] ) [: ~. [: /:~"1 (]#[:i.]) ,."0 *:$i.) > NB. 2 item list has one pair with indices 0 and 1 > pairi 2 > 0 1 > NB. 3 item list has 3 pairs with these indices: > pairi 3 > 0 1 > 0 2 > 1 2 > NB. 4 item list has 6 pairs with these indices: > pairi 4 > 0 1 > 0 2 > 0 3 > 1 2 > 1 3 > 2 3 > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > > > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
