Comment by dzaima

Unless the interpreter is capable of pattern-recognizing that whole pattern, that will be less efficient, e.g. having to work with 16-bit integers for x in the range 128..32767, whereas the direct version can construct the array directly (i.e. one byte or bit per element depending on whether kdb has bit booleans). Can't provide timings for kdb for licensing reasons, but here's Dyalog APL and CBQN doing the same thing, showing the fast version at 3.7x and 10.5x faster respectively: https://dzaima.github.io/paste/#0U1bmUlaOVncM8FGP5VIAg0e9cxV...