Optimizing Transposition of large NumPy arrays

Last update on March 27 2025 09:14:50 (UTC/GMT +8 hours)

6. Large 2D Array Transpose Optimization

Write a NumPy program that creates a function to transpose a large 2D NumPy array using nested for loops. Optimize it using NumPy's transpose() function.

Sample Solution:

Python Code:

import numpy as np

# Create a large 2D NumPy array with shape (1000, 1000)
large_array = np.random.rand(1000, 1000)

# Function to transpose a 2D array using nested for loops
def transpose_using_loops(array):
    rows, cols = array.shape
    transposed_array = np.zeros((cols, rows))
    for i in range(rows):
        for j in range(cols):
            transposed_array[j, i] = array[i, j]
    return transposed_array

# Transpose the array using the nested for loops
transposed_loop = transpose_using_loops(large_array)
print("Transposed array using for loop (first 5x5 block):\n", transposed_loop[:5, :5])

# Optimize the transposition using NumPy's transpose() function
transposed_numpy = np.transpose(large_array)
print("Transposed array using NumPy's transpose() function (first 5x5 block):\n", transposed_numpy[:5, :5])

Output:

Transposed array using for loop (first 5x5 block):
 [[0.40551353 0.40558167 0.86467457 0.58567322 0.8239284 ]
 [0.3031671  0.45184241 0.5199638  0.52295596 0.52545074]
 [0.40211577 0.25829343 0.6505094  0.60260168 0.49010591]
 [0.42364773 0.85953907 0.24050983 0.50997478 0.54401922]
 [0.94613512 0.94341257 0.30700166 0.25956794 0.17429532]]
Transposed array using NumPy's transpose() function (first 5x5 block):
 [[0.40551353 0.40558167 0.86467457 0.58567322 0.8239284 ]
 [0.3031671  0.45184241 0.5199638  0.52295596 0.52545074]
 [0.40211577 0.25829343 0.6505094  0.60260168 0.49010591]
 [0.42364773 0.85953907 0.24050983 0.50997478 0.54401922]
 [0.94613512 0.94341257 0.30700166 0.25956794 0.17429532]]

Explanation:

• Create a large array: A 2D NumPy array with shape (1000, 1000) is created using np.random.rand().
• Function with nested for loops: A function transpose_using_loops transposes the array using nested for loops.
• Transpose with loops: The array is transposed using the nested for loops, and the first 5x5 block of the result is printed.
• Optimize with NumPy: The transposition is optimized using NumPy's built-in transpose() function, and the first 5x5 block of the result is printed.

For more Practice: Solve these Related Problems:

• Write a Numpy program to transpose a large 2D array using nested loops, then optimize it with np.transpose.
• Write a Numpy program to manually swap rows and columns of a large 2D array using loops, then optimize using np.swapaxes.
• Write a Numpy program to create a transposed copy of a large 2D array via for loops, then optimize using np.ascontiguousarray.
• Write a Numpy program to compute a custom axis reordering for a large 2D array using loops, then optimize with np.moveaxis.

Python-Numpy Code Editor:

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