There are 5 shapes on a 4x4 grid. Which shape is closest to the purple square in terms of Manhattan distance? The final answer is the grid position of the closest shape like (row_index, column_index).
<think>Target shape: purple square at (1, 3)
Distance from target shape to orange right_triangle at (3, 1): 4
Distance from target shape to green right_triangle at (1, 1): 2
Distance from target shape to blue right_triangle at (0, 2): 2
Distance from target shape to red rectangle at (0, 1): 3
Closest shape is the green right_triangle at (1, 1) with distance 2</think>

<answer>(1, 1)</answer>