fix(vision/cifar): copy on indexing

example/tensor-index/main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"github.com/sugarme/gotch"
 	"github.com/sugarme/gotch/tensor"
 )
 
@@ -46,4 +47,14 @@ func main() {
 
 	combinedTs.Print()
 
+	// Copy to index
+	desTs := tensor.MustZeros([]int64{5}, gotch.Float.CInt(), gotch.CPU.CInt())
+	srcTs := tensor.MustOnes([]int64{1}, gotch.Float.CInt(), gotch.CPU.CInt())
+	idx := tensor.NewNarrow(0, 3)
+
+	// NOTE: indexing operations return view on the same memory
+	desTs.Print()
+	desTs.Idx(idx).MustView([]int64{-1}, false).Copy_(srcTs)
+	desTs.Print()
+
 }

tensor/index.go

@@ -58,6 +58,9 @@ package tensor
 // is that `i` guarantees the input and result tensor shares the same
 // underlying storage, while NumPy may copy the tensor in certain scenarios.
 
+// NOTE: select, narrow and indexing operations (except when using a LongTensor index) return views onto the same memory.
+// https://discuss.pytorch.org/t/does-select-and-narrow-return-a-view-or-copy/289
+
 import (
 	"fmt"
 	"log"

vision/cifar.go

@@ -59,12 +59,11 @@ func readFile(filename string) (imagesTs ts.Tensor, labelsTs ts.Tensor) {
 		tmp1 := content.MustNarrow(0, int64(1+contentOffset), int64(bytesPerImage-1), false)
 		tmp2 := tmp1.MustView([]int64{cfC, cfH, cfW}, true)
 		tmp3 := tmp2.MustTo(gotch.CPU, true)
-		selectImageTs := images.Idx(ts.NewSelect(int64(idx)))
-		selectImageTs.Copy_(tmp3)
-		tmp3.MustDrop()
 
-		// TODO: concat all selectLabelTs and selectImageTs to single labelsTs and
-		// imagesTs
+		// NOTE: tensor indexing operations return view on the same memory
+		// images.Idx(ts.NewSelect(int64(idx))).Copy_(tmp3)
+		images.Idx(ts.NewSelect(int64(idx))).MustView([]int64{cfC, cfH, cfW}, false).Copy_(tmp3)
+		tmp3.MustDrop()
 	}
 
 	tmp1 := images.MustTotype(gotch.Float, true)