From 040ccc1089d4745b3b50157fb07dddc071dd1553 Mon Sep 17 00:00:00 2001
From: Martin Holters <martin.holters@hsu-hh.de>
Date: Fri, 23 Mar 2018 08:16:48 +0100
Subject: [PATCH] Add `selectdim` (#522)

---
 README.md        |  2 ++
 src/Compat.jl    | 11 +++++++++++
 test/runtests.jl | 10 ++++++++++
 3 files changed, 23 insertions(+)

diff --git a/README.md b/README.md
index 7def7efee..4b60fff22 100644
--- a/README.md
+++ b/README.md
@@ -291,6 +291,7 @@ Currently, the `@compat` macro supports the following syntaxes:
   `Compat.median`, `Compat.minimum`, `Compat.prod`, `Compat.reduce`, `Compat.sort`,
   `Compat.std`, `Compat.sum`, `Compat.var`, and `Compat.varm` with `dims` keyword argument ([#25989],[#26369]).
 
+* `selectdim` to obtain a view of an array with a specified index for a specified dimension ([#26009]).
 
 ## Renaming
 
@@ -607,6 +608,7 @@ includes this fix. Find the minimum version from there.
 [#25989]: https://github.com/JuliaLang/julia/issues/25989
 [#25990]: https://github.com/JuliaLang/julia/issues/25990
 [#25998]: https://github.com/JuliaLang/julia/issues/25998
+[#26009]: https://github.com/JuliaLang/julia/issues/26009
 [#26069]: https://github.com/JuliaLang/julia/issues/26069
 [#26089]: https://github.com/JuliaLang/julia/issues/26089
 [#26149]: https://github.com/JuliaLang/julia/issues/26149
diff --git a/src/Compat.jl b/src/Compat.jl
index f1835344f..c60daaed2 100644
--- a/src/Compat.jl
+++ b/src/Compat.jl
@@ -1778,6 +1778,17 @@ if VERSION < v"0.7.0-DEV.4534"
         dims===nothing ? Base.reverse(a) : Base.flipdim(a, dims)
 end
 
+if !isdefined(Base, :selectdim) # 0.7.0-DEV.3976
+    export selectdim
+    @inline selectdim(A::AbstractArray, d::Integer, i) = _selectdim(A, d, i, Base.setindex(axes(A), i, d))
+    @noinline function _selectdim(A, d, i, idxs)
+        d >= 1 || throw(ArgumentError("dimension must be ≥ 1"))
+        nd = ndims(A)
+        d > nd && (i == 1 || throw(BoundsError(A, (ntuple(k->Colon(),d-1)..., i))))
+        return view(A, idxs...)
+    end
+end
+
 include("deprecated.jl")
 
 end # module Compat
diff --git a/test/runtests.jl b/test/runtests.jl
index fe5e3c898..cb365e650 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1673,4 +1673,14 @@ end
 @test length(Compat.CartesianIndices((1:2,))) == 2
 @test length(Compat.CartesianIndices((1:2, -1:1))) == 6
 
+# 0.7.0-DEV.3976
+let A = rand(5,5)
+    @test selectdim(A, 1, 3) == A[3, :]
+    @test selectdim(A, 1, 1:3) == A[1:3, :]
+    @test selectdim(A, 2, 3) == A[:, 3]
+    @test selectdim(A, 2, 1:3) == A[:, 1:3]
+    selectdim(A, 1, 3)[3] = 42
+    @test A[3,3] == 42
+end
+
 nothing