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Concatenate Arrays

EasyNumPy Manipulation

Problem Statement

Combine multiple NumPy arrays along different axes.

Background

  • np.concatenate([arr1, arr2], axis=0): Stack vertically (default)
  • np.concatenate([arr1, arr2], axis=1): Stack horizontally
  • np.vstack(): Vertical stack
  • np.hstack(): Horizontal stack

Your Task

Write a function concat_arrays(arr1, arr2) that returns a dictionary with:

  • "vstack": Vertically stacked array as nested list
  • "hstack": Horizontally stacked array as nested list
  • "vstack_shape": Shape of vstack result as list
  • "hstack_shape": Shape of hstack result as list

Output Format

Return a dictionary with exactly these four keys.

Example:

Input:
arr1 = [[1, 2], [3, 4]], arr2 = [[5, 6], [7, 8]]
Output:
{'vstack': [[1, 2], [3, 4], [5, 6], [7, 8]], 'hstack': [[1, 2, 5, 6], [3, 4, 7, 8]], 'vstack_shape': [4, 2], 'hstack_shape': [2, 4]}
Reasoning:

vstack: 2 rows + 2 rows = 4 rows. hstack: 2 cols + 2 cols = 4 cols

Constraints:

  • Use np.vstack() and np.hstack()
  • Both arrays will have compatible shapes
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Test Results

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