ValueError: Expected 2D array, got scalar array instead

ValueError: expected 2D got scalar

$ python -c "from sklearn.preprocessing import StandardScaler; StandardScaler().fit(1.0)"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
TypeError: 'float' object is not iterable

Why this happens

• Passing a single number instead of a 2D array.

Fix

• Reshape to 2D with shape (n_samples, n_features).

Wrong code

StandardScaler().fit(1.0)

Fixed code

import numpy as np
StandardScaler().fit(np.array([[1.0],[2.0],[3.0]]))