From 8f49600a6b717ada5973d518a9f042a4f2f8c58b Mon Sep 17 00:00:00 2001
From: pkoppstein <pkoppstein@gmail.com>
Date: Mon, 24 Jul 2023 20:12:23 -0400
Subject: [PATCH] builtin.jq: simpler and faster transpose (#2758)

---
 src/builtin.jq | 9 +--------
 tests/jq.test  | 4 ++++
 2 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/src/builtin.jq b/src/builtin.jq
index a13d7845..45ba3060 100644
--- a/src/builtin.jq
+++ b/src/builtin.jq
@@ -181,14 +181,7 @@ def combinations(n):
       | combinations;
 # transpose a possibly jagged matrix, quickly;
 # rows are padded with nulls so the result is always rectangular.
-def transpose:
-  if . == [] then []
-  else . as $in
-  | (map(length) | max) as $max
-  | length as $length
-  | reduce range(0; $max) as $j
-      ([]; . + [reduce range(0;$length) as $i ([]; . + [ $in[$i][$j] ] )] )
-  end;
+def transpose: [range(0; map(length)|max // 0) as $i | [.[][$i]]];
 def in(xs): . as $x | xs | has($x);
 def inside(xs): . as $x | xs | contains($x);
 def repeat(exp):
diff --git a/tests/jq.test b/tests/jq.test
index 4e0b950d..466d1850 100644
--- a/tests/jq.test
+++ b/tests/jq.test
@@ -1487,6 +1487,10 @@ transpose
 [[1], [2,3]]
 [[1,2],[null,3]]
 
+transpose
+[]
+[]
+
 ascii_upcase
 "useful but not for é"
 "USEFUL BUT NOT FOR é"