From e72c3605b252322a145c928b65ff46bba2ccd9d1 Mon Sep 17 00:00:00 2001
From: Marshall Lochbaum <mwlochbaum@gmail.com>
Date: Mon, 3 Aug 2020 16:23:51 -0400
Subject: Faster list-of-lists join

---
 impl.bqn | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

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
-- 
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