Did you mean? 1/0 |domain error | 1 /0 |[-0] 1%0 _
What made me think of sparse arrays is that it does much of the leg work to identify some number, like zero, to remove. It keeps an index list of elements not removed and has tools to extract only those elements not removed. It's really not what sparse ($.) is intended for, but I thought it might be useful in this case. In my thinking, unknown values should never be put in an array. Having them in an array leads to so many problems, only a few have been mentioned in this thread. If "unknown values" are generated as part of the computation then it seems to me it is time to go back and look at the problem analysis. ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
