From 7597c37e034d5365e08789b058acb3ab0372bd50 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?David=20M=C3=BCller-Widmann?=
 <devmotion@users.noreply.github.com>
Date: Tue, 16 Jun 2026 15:07:05 +0200
Subject: [PATCH 1/2] Fix `var`/`std` along a dimension with `UnitWeights`

`var(A::AbstractArray, w::UnitWeights, dim::Int)` (and therefore `std`
along a dimension, which dispatches to it) compared the weight length
against the *total* number of array elements (`length(v)`) instead of the
size along the reduction dimension (`size(v, dim)`).

As a result the method threw `DimensionMismatch("Inconsistent array
lengths.")` for essentially any multidimensional array, e.g.

    var(reshape(1.0:12.0, 3, 4), uweights(3), 1)

even though the weight vector correctly matched the reduced dimension.

Compare against `size(v, dim)`, consistent with the existing
`mean(A, w::UnitWeights; dims)` method, and add regression tests covering
weighted `var`/`std` along a dimension with `UnitWeights`.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 Project.toml    |  2 +-
 src/moments.jl  |  2 +-
 test/moments.jl | 16 ++++++++++++++++
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/Project.toml b/Project.toml
index e1c2daed1..07569e162 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,6 +1,6 @@
 name = "StatsBase"
 uuid = "2913bbd2-ae8a-5f71-8c99-4fb6c76f3a91"
-version = "0.34.11"
+version = "0.34.12"
 authors = ["JuliaStats"]
 
 [deps]
diff --git a/src/moments.jl b/src/moments.jl
index 04de97a83..dcfe1e6b7 100644
--- a/src/moments.jl
+++ b/src/moments.jl
@@ -73,7 +73,7 @@ function var(A::AbstractArray{<:Real}, w::AbstractWeights, dim::Int; mean=nothin
 end
 function var(v::AbstractArray{<:Real}, w::UnitWeights, dim::Int; mean=nothing,
                   corrected::Union{Bool, Nothing}=nothing)
-    length(w) == length(v) || throw(DimensionMismatch("Inconsistent array lengths."))
+    size(v, dim) == length(w) || throw(DimensionMismatch("Inconsistent array lengths."))
     corrected = depcheck(:var, :corrected, corrected)
     return var(v; mean, corrected, dims=dim)
 end
diff --git a/test/moments.jl b/test/moments.jl
index a3402b965..fd4ad33c2 100644
--- a/test/moments.jl
+++ b/test/moments.jl
@@ -481,4 +481,20 @@ end
     end
 end
 
+@testset "weighted var/std along a dimension with UnitWeights" begin
+    x = reshape(collect(1.0:12.0), 3, 4)
+
+    # `UnitWeights` along a dimension must match the unweighted result and must
+    # not erroneously compare the weight length against the total array length.
+    @test var(x, uweights(3), 1; corrected=true) ≈ var(x; dims=1)
+    @test var(x, uweights(4), 2; corrected=true) ≈ var(x; dims=2)
+    @test var(x, uweights(3), 1; corrected=false) ≈ var(x; dims=1, corrected=false)
+    @test std(x, uweights(3), 1; corrected=true) ≈ std(x; dims=1)
+    @test std(x, uweights(4), 2; corrected=true) ≈ std(x; dims=2)
+
+    # A weight vector whose length does not match the reduction dimension errors.
+    @test_throws DimensionMismatch var(x, uweights(4), 1; corrected=true)
+    @test_throws DimensionMismatch var(x, uweights(3), 2; corrected=true)
+end
+
 end # @testset "StatsBase.Moments"

From d930fdbe6906cdd7d3c164e94ce3d70e78093fce Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?David=20M=C3=BCller-Widmann?=
 <devmotion@users.noreply.github.com>
Date: Wed, 17 Jun 2026 07:19:26 +0200
Subject: [PATCH 2/2] Update test/moments.jl

---
 test/moments.jl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/moments.jl b/test/moments.jl
index fd4ad33c2..6ba730707 100644
--- a/test/moments.jl
+++ b/test/moments.jl
@@ -482,7 +482,7 @@ end
 end
 
 @testset "weighted var/std along a dimension with UnitWeights" begin
-    x = reshape(collect(1.0:12.0), 3, 4)
+    x = reshape(1.0:12.0, 3, 4)
 
     # `UnitWeights` along a dimension must match the unweighted result and must
     # not erroneously compare the weight length against the total array length.