1D NumPy 配列を転置するとどうなりますか?

Transpose of a 1D NumPy Array

When working with NumPy arrays, it's important to understand the effects of transposition. Typically, the transpose of an array exchanges its rows and columns, resulting in a new array with swapped dimensions. However, in the case of a 1D array, the transpose operation has a different impact.

Consider the following Python snippet:

import numpy as np
a = np.array([5,4])
print(a)
print(a.T)

Instead of transposing the array, it remains unchanged. This is because the transpose of a 1D array is inherently a 1D array. Unlike in MATLAB, where "1D" arrays are effectively 2D, NumPy treats 1D arrays distinctly.

If you require a transposed 2D representation of your 1D vector, you can achieve it by slicing the vector using np.newaxis:

import numpy as np
a = np.array([5,4])[np.newaxis]
print(a)
print(a.T)

Now, the a.T operation will produce a transposed 2D array.

It's worth noting that adding an extra dimension to a 1D vector is not always necessary. In most cases, NumPy automatically broadcasts 1D arrays for appropriate calculations, eliminating the need to explicitly distinguish between row and column vectors.

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