From np.array([1, 2, 3]), produce [1, 1, 2, 2, 3, 3] — each element doubled in…

NumPy · from Joining and splitting arrays

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Exercise 4

From np.array([1, 2, 3]), produce [1, 1, 2, 2, 3, 3] — each element doubled in place.

your answer
stuck? the lesson behind it
Joining and splitting arrays
concatenate extends an axis; stack creates one. Everything else is shorthand.