argrelextrema returns tuple of 2 empty arrays when no peaks found in 1D vector

[dmcminniwc]

When using the scipy.signal.argrelextrema function to find the peaks in a 1D numpy vector and no peaks are found the return value is a tuple with two empty arrays.

The docs say it returns "Indices of the maxima, as an array of integers". I would expect with no peaks it would be a tuple with one empty array for each dimension of the input vector.

For example:

import numpy as np
import scipy.signal as sig
y = np.concatenate([np.arange(1, 0, -0.01), np.arange(0, 1, 0.01)]) 
peaks = sig.argrelextrema(0.5-np.abs(y - 0.5), np.greater)
print peaks # Prints '(array([ 50, 150]),)'
peaks = sig.argrelextrema(y, np.greater) # No peaks
print peaks # Prints '((array([]), dtype=float64),(array([]), dtype=float64),)'

I would have expected '((array([]), dtype=float64),)' for the second print statement.

In the source for scipy it returns "(np.array([]),) * 2" when no peaks are found but it should probably be "(np.array([]),) * data.ndim".

[dmcminniwc]

I forgot to add that this was using scipy v 0.12.0 on Windows 7 x64 Professional, running on python 2.7.5.

[sebix]

This issue has been discussed on the Scipy-User Mailinglist: http://mail.scipy.org/pipermail/scipy-user/2013-September/034905.html

[WarrenWeckesser]

This is fixed by #2836