Array Reshaping

Turn a 1D array of 6 elements into a 2×3 matrix:

import numpy as np
arr = np.arange(6)
print(arr)
matrix = arr.reshape(2, 3)
print(matrix)

Python

Output

Pass -1 for one dimension and NumPy calculates it automatically:

import numpy as np
arr = np.arange(12)
# NumPy infers the 2nd dimension
a = arr.reshape(3, -1)
print(a.shape)
b = arr.reshape(-1, 4)
print(b.shape)

Python

Output

flatten() converts any array back to 1D, row by row:

import numpy as np
matrix = np.array([[1, 2, 3],
                   [4, 5, 6]])
flat = matrix.flatten()
print(flat)

Python

Output

Combining np.arange() with reshape() is a common pattern for creating structured arrays:

import numpy as np
grid = np.arange(1, 10).reshape(3, 3)
print(grid)

Python

Output

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