CODEWITHSUNDEEP
pythonnumpypiecewise
Xeno
Xeno

Reputation: 11

np.piecewise does not work with three conditions

i am very new to python and need to define a piecewise funtion, however, as soon as i specify more than two conditions i am greeted with "ValueError: function list and condition list must be the same".

For example, the very basic test function

def test(r):
    r1=1.8
    return np.piecewise(r, [(r<r1), (r==r1), (r>r1)], [0, 1, 2])

produces this error, whereas a function with only two conditions

def test(r):
    r1=1.8
    return np.piecewise(r, [(r<r1), (r>r1)], [0, 2])

works flawlessly. I circumvented my problem by using np.select, however, i am curious as to what my mistake is and how to resolve it. I am not sure if this of interest, but the variable "r" used in the function is going to be a scalar value, not a list or array or something complicated.

Does anyone have an idea how to resolve my problem?

Upvotes: 1

Views: 1393

Answers (1)

Crist&#243;bal Sif&#243;n
Crist&#243;bal Sif&#243;n

Reputation: 568

you are passing a list to the function but you should pass a numpy array:

r1 = 1.8
r = numpy.arange(0, 3, 0.2)
print numpy.piecewise(r, [(r<r1), (r==r1), (r>r1)], [0, 1, 2])
# prints:
# array([ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  1.,  2.,  2.,  2., 2.,  2.])

but adding

r = list(r)
print numpy.piecewise(r, [(r<r1), (r==r1), (r>r1)], [0, 1, 2])

gives the error you mention.

Upvotes: 3

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