Faster list-of-lists join

1 files changed, 6 insertions, 1 deletions

diff --git a/impl.bqn b/impl.bqn
index 79c64fa3..6efef2c6 100644
--- a/impl.bqn
+++ b/impl.bqn
@@ -256,7 +256,12 @@ Replicate ← {0<=𝕨}◶(⥊˜⟜≠Rep⊢)‿{!𝕨=○≠𝕩⋄𝕨Rep𝕩}
 #⌜
 # LAYER 6: Everything else
 
-Join←{
+Join←(1≠=)◶⟨∨´1≠=¨,1⟩◶{
+  # List of lists
+  i←j←¯1⋄e←⟨⟩⋄a←𝕩
+  {{e↩a⊑˜i↩𝕩⋄j↩¯1}⍟(i⊸≠)𝕩⋄(j↩j+1)⊑e}¨/≠¨𝕩
+}‿{
+  # Multidimensional
   C←(<⟨⟩)⥊⊸∾⌜´⊢  # Cartesian array product
   ! IsArray 𝕩
   s←≢¨𝕩