From cadb9171b11db6f22291254843c64fe49ebbf091 Mon Sep 17 00:00:00 2001
From: Daniel Strobusch <1847260+dastrobu@users.noreply.github.com>
Date: Sat, 18 Jan 2020 13:54:07 +0100
Subject: [PATCH] fix single slice gives empty array instead of single element
 array

closes #1.
---
 Sources/NdArray/NdArray.swift           | 15 +++++++++++----
 Tests/NdArrayTests/subscriptTests.swift |  8 ++++++++
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/Sources/NdArray/NdArray.swift b/Sources/NdArray/NdArray.swift
index eee197a..197c82b 100644
--- a/Sources/NdArray/NdArray.swift
+++ b/Sources/NdArray/NdArray.swift
@@ -65,7 +65,7 @@ open class NdArray<T>: CustomDebugStringConvertible,
     internal convenience init(empty shape: [Int], order: Contiguous = .C) {
         let n = shape.isEmpty ? 0 : shape.reduce(1, *)
         self.init(empty: n)
-        var success  = reshape([n])
+        var success = reshape([n])
         assert(success, "could not reshape from [\(self.shape)] to \(n)")
         success = reshape(shape, order: order)
         assert(success, "could not reshape form [\(self.shape)] to \(shape)")
@@ -386,9 +386,16 @@ open class NdArray<T>: CustomDebugStringConvertible,
             // here we reduce the shape, hence slice = 0
             let slice = NdArraySlice(self, startIndex: startIndex, sliced: 0)
             // drop leading shape 1
-            slice.shape = Array(slice.shape[1...])
-            slice.strides = Array(slice.strides[1...])
-            slice.count = slice.len
+            let shape = [Int](slice.shape[1...])
+            if shape.isEmpty {
+                slice.shape = [1]
+                slice.strides = [1]
+                slice.count = 1
+            } else {
+                slice.shape = shape
+                slice.strides = Array(slice.strides[1...])
+                slice.count = slice.len
+            }
             return slice
         }
         set {
diff --git a/Tests/NdArrayTests/subscriptTests.swift b/Tests/NdArrayTests/subscriptTests.swift
index ff1fcd0..408425d 100644
--- a/Tests/NdArrayTests/subscriptTests.swift
+++ b/Tests/NdArrayTests/subscriptTests.swift
@@ -935,4 +935,12 @@ class NdArraySliceSubscriptTests: XCTestCase {
             XCTAssertEqual(NdArray(copy: a[0], order: .C).dataArray, [0, 1, 2, 3, 4, 5])
         }
     }
+
+    func testSingleElementSlice1d() {
+        let a = NdArray<Double>.range(to: 4)
+        let s: NdArraySlice<Double> = a[2]
+        XCTAssertEqual(s.shape, [1])
+        XCTAssertEqual(s.dataArray, [2])
+    }
+
 }