> Sure, we can replace zeros with infinity and vice versa before and after > division. But, can it be avoided? What I am looking for is conditional
Why do you want to avoid it? I suggest simply: f=: %*0~:] x f y 0 2 1 0.666667 On Sat, May 18, 2013 at 10:13 AM, P T <[email protected]> wrote: > Thanks Devon and Robert. > > Sure, we can replace zeros with infinity and vice versa before and after > division. But, can it be avoided? What I am looking for is conditional > division without writing an explicit loop. My intention is to represent an > electrical transmission network with matrices and they can potentially be > large. I am trying to minimizing the number of operations. > > I am reading on sparse matrices in "Learning J" by Roger Stokes and looks > like it can do what I am looking for. But, I am not sure if it actually > does not perform the unnecessary operations (i.e. division by zeros) or > just a display issue. > > x =: 1 $. 6 6 NB. an empty 6x6 matrix > x =: 4 5 6 7 ( 0 0 ; 1 1; 2 2; 3 3) } x NB. insert some data > x > 0 0 │ 4 > 1 1 │ 5 > 2 2 │ 6 > 3 3 │ 7 > > y =: 1 $. 6 6 > y =: 1 2 3 4 ( 0 0 ; 1 1; 2 2; 3 3) } y > y > 0 0 │ 1 > 1 1 │ 2 > 2 2 │ 3 > 3 3 │ 4 > > x%y > 0 0 │ 4 > 1 1 │ 2.5 > 2 2 │ 2 > 3 3 │ 1.75 > > Thanks, > PT > > > > On Fri, May 17, 2013 at 6:45 PM, Robert Knight <[email protected] > >wrote: > > > *PT-* > > > > To modify the (infinite) "zero-division" result from *infinity* to > > *zero*... > > > > How about adding infinity to the divisor's zero-elements? > > > > *z =: x%y+_*y=0* > > > > > > ]x =. 2 2 $ 2 > > > > 2 2 > > 2 2 > > > > ]y =. 2 2 $ i.4 > > > > 0 1 > > 2 3 > > > > ]z =. x%y+_*y=0 > > > > 0 2 > > 1 0.666667 > > > > *-Robert Knight* > > (Also a J-newbie) > > > > > > On Fri, May 17, 2013 at 6:44 PM, P T <[email protected]> wrote: > > > > > > > I am learning J (J602) and dividing one table with another. When > division > > > by zero occurs, I want the the value to be zero instead of infinity. > For > > > example, in the results below, I want the first element to be 0.0 > instead > > > of _ > > > > > > ]x =. 2 2 $ 2 > > > 2 2 > > > 2 2 > > > > > > ]y=. 2 2 $ i.4 > > > 0 1 > > > 2 3 > > > > > > x%y > > > _ 2 > > > 1 0.666667 > > > > > > > > > May be I can replace all occurrences of _ with 0.0. But, can I avoid > this > > > additional step? > > > > > > Thanks, > > > PT > > > ---------------------------------------------------------------------- > > > For information about J forums see http://www.jsoftware.com/forums.htm > > > > > ---------------------------------------------------------------------- > > For information about J forums see http://www.jsoftware.com/forums.htm > > > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
