Lightly tested and non-optimized and ugly, but seems to work! genseq=:({: + i.@:>:@:-/)@]

seq =: (] (>/@[ \:~@]^:[ genseq) \:~) f. ] (>/@[ \:~@]^:[ ({: + i.@:>:@:-/)@]) \:~ seq 3 7 3 4 5 6 7 seq 7 3 7 6 5 4 3 On Fri, Apr 6, 2018 at 3:23 PM, Devon McCormick <devon...@gmail.com> wrote: > Hi - > > I'm working with selecting sequential items from a vector given a starting > and an ending point as a pair of integers. If we assume we always get the > pair as (lesser, greater), something like this suffices: > > seq=: {. + [: i. [: >: -~/ > seq 3 7 > 3 4 5 6 7 > > However, if our assumption about the order of our points is violated, we > get nonsense: > > seq 7 3 > 7 8 9 > > Just for robustness, how could we write a version of "seq" that would > return the sequence in reverse order in this latter case, i.e. give the > proper sequence from seven to three: 7 6 5 4 3 ? > > I generalized the "seq" verb to remove the ordering assumption: my idea was > to generate the ascending sequence, then flip it if >/y is true. I tried > this with "agenda" but am not sure how to get it to work on one thing - the > ascending vector - on the basis of comparison of another thing - the pair > of integers. > > I did achieve this using the "power" conjunction: > > seq=: 3 : '|.^:(>/y)](<./ + [: i. [: >: >./ - <./) y' > seq 3 7 > 3 4 5 6 7 > seq 7 3 > 7 6 5 4 3 > > Does anyone have any ideas for a more elegant, preferably tacit, solution? > > Thanks, > > Devon > -- > > Devon McCormick, CFA > > Quantitative Consultant > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm