From 91d837940903c2fb03eef8db609e0a531970f56f Mon Sep 17 00:00:00 2001
From: Ilya Pekelny <pekelny@gmail.com>
Date: Sat, 14 Apr 2018 18:24:15 +0300
Subject: [PATCH] Transpose matrix with allocation of a new one

---
 matrix.go      | 19 +++++++++++++++++++
 matrix_test.go | 43 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 62 insertions(+)

diff --git a/matrix.go b/matrix.go
index 2d1ef17..1a34718 100644
--- a/matrix.go
+++ b/matrix.go
@@ -77,3 +77,22 @@ func OuterProduct(column, row []float64) (output [][]float64) {
 	}
 	return
 }
+
+func Transpose(matrix [][]float64, lineSize int) (output [][]float64, err error) {
+	output = make([][]float64, lineSize)
+	for i, v := range matrix {
+		if len(v) != lineSize {
+			err = fmt.Errorf(
+				"Inconsistent matrix line size. Expected: %d. Actual: %d",
+				lineSize, len(v),
+			)
+			return
+		}
+		for j := range v {
+			// To do transpose in place switch matrix items
+			//matrix[i][j], matrix[j][i] = matrix[j][j], matrix[i][j]
+			output[j] = append(output[j], matrix[i][j])
+		}
+	}
+	return
+}
diff --git a/matrix_test.go b/matrix_test.go
index 75d72e0..d1fd5de 100644
--- a/matrix_test.go
+++ b/matrix_test.go
@@ -189,3 +189,46 @@ func TestEntrywiseSum(t *testing.T) {
 		})
 	}
 }
+
+func TestTranspose(t *testing.T) {
+	type args struct {
+		matrix   [][]float64
+		lineSize int
+	}
+	tests := []struct {
+		name       string
+		args       args
+		wantOutput [][]float64
+		wantErr    bool
+	}{
+		{
+			name: "transpose",
+			args: args{
+				[][]float64{
+					{1, 2, 3, 4},
+					{1, 2, 3, 4},
+					{1, 2, 3, 4},
+				},
+				4,
+			},
+			wantOutput: [][]float64{
+				{1, 1, 1},
+				{2, 2, 2},
+				{3, 3, 3},
+				{4, 4, 4},
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotOutput, err := Transpose(tt.args.matrix, tt.args.lineSize)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("Transpose() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if !reflect.DeepEqual(gotOutput, tt.wantOutput) {
+				t.Errorf("Transpose() = %v, want %v", gotOutput, tt.wantOutput)
+			}
+		})
+	}
+}