From 8a1e018a0c972b578da059d163bc22c13eda2ed0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bogumi=C5=82=20Kami=C5=84ski?= <bkamins@sgh.waw.pl>
Date: Tue, 9 Apr 2024 23:45:10 +0200
Subject: [PATCH] add tests and news

---
 NEWS.md        |  3 +++
 test/select.jl | 18 ++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/NEWS.md b/NEWS.md
index 22d2045f0..1d7fd3050 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -42,6 +42,9 @@
 * Ensure that `allunique(::AbstractDataFrame, ::Any)` always gets
   interpreted as test for uniqueness of rows in the first positional argument
   ([#3434](https://github.com/JuliaData/DataFrames.jl/issues/3434))
+* Make sure that an empty vector of `Any` or of `AbstractVector` is treated as having
+  no columns when a data frame is being processed with `combine`/`select`/`transform`.
+  ([#3435](https://github.com/JuliaData/DataFrames.jl/issues/3435))
 
 # DataFrames.jl v1.6.1 Release Notes
 
diff --git a/test/select.jl b/test/select.jl
index 67f97df2f..3a8ad3b23 100644
--- a/test/select.jl
+++ b/test/select.jl
@@ -3024,4 +3024,22 @@ end
     @test_throws ArgumentError combine(gdf, :x => (x -> x[1] == 2 ? "x" : cr) => AsTable)
 end
 
+@testset "empty vector" begin
+    df = DataFrame(a=1:3)
+
+    @test_throws ArgumentError select(df, :a => (x -> Vector{Any}[]))
+
+    for T in (Vector{Any}, Any, NamedTuple{(:x,),Tuple{Int64}})
+        v = combine(df, :a => (x -> T[])).a_function
+        @test isempty(v)
+        @test eltype(v) === T
+    end
+
+    @test size(combine(df, :a => (x -> Vector{Any}[]) => AsTable)) == (0, 0)
+    @test size(combine(df, :a => (x -> Any[]) => AsTable)) == (0, 0)
+    df2 = combine(df, :a => (x -> NamedTuple{(:x,),Tuple{Int64}}[]) => AsTable)
+    @test size(df2) == (0, 1)
+    @test eltype(df2.x) === Int
+end
+
 end # module