Concatenating two one-dimensional NumPy arrays
The line should be:
The arrays you want to concatenate need to be passed in as a sequence, not as separate arguments.
From the NumPy documentation:
numpy.concatenate((a1, a2, ...), axis=0)
Join a sequence of arrays together.
It was trying to interpret your
b as the axis parameter, which is why it complained it couldn't convert it into a scalar.
There are several possibilities for concatenating 1D arrays, e.g.,
numpy.r_[a, a],numpy.stack([a, a]).reshape(-1),numpy.hstack([a, a]),numpy.concatenate([a, a])
All those options are equally fast for large arrays; for small ones,
concatenate has a slight edge:
The plot was created with perfplot:
import numpyimport perfplotperfplot.show( setup=lambda n: numpy.random.rand(n), kernels=[ lambda a: numpy.r_[a, a], lambda a: numpy.stack([a, a]).reshape(-1), lambda a: numpy.hstack([a, a]), lambda a: numpy.concatenate([a, a]), ], labels=["r_", "stack+reshape", "hstack", "concatenate"], n_range=[2 ** k for k in range(19)], xlabel="len(a)",)