crippledlambda crippledlambda - 1 year ago 192
Python Question

Ternary operator for NumPy ndarray?

Does NumPy have a ternary operator? For instance, in R there is a vectorized


> ifelse(1:10 < 3,"a","b")
[1] "a" "a" "b" "b" "b" "b" "b" "b" "b" "b"

Is there anything equivalent in NumPy?

Answer Source

You are looking for numpy.where():

>>> print numpy.where(numpy.arange(10) < 3, 'a', 'b')
['a', 'a', 'a', 'b', 'b', 'b', 'b', 'b', 'b', 'b']

NumPy even has a generalization (that maps 0, 1, 2, etc. to values, instead of mapping only True and False): numpy.choose().

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