Thanks for all the answers so far. What prompted my questioning is the Advent of Code problem mentioned by R.E.Boss in september : http://www.jsoftware.com/pipermail/programming/2019-September/053995.html
I tried a simple approach splitting huge arrays in two to insert data and it took forever to execute. Using a simple simulation of a linked lisI decreased execution time by orders of magnitude (2 minutes versus 3 days !). Viewing arrays as memory, as suggested by Raul, is probably the appropriate mindset. ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
