I have a (3,3) numpy array and would like to figure out the sign of the element whose absolute value is maximum:
X = [[-2.1, 2, 3],
[ 1, -6.1, 5],
[ 0, 1, 1]]
s = numpy.argmax(numpy.abs(X),axis=0)
gives me the indices of the elements that I need, s = [ 0,1,1].
How can I use this array to extract the elements [ -2.1, -6.1, 5] to figure out their sign?
Try this:
# You might need to do this to get X as an ndarray (for example if X is a list)
X = numpy.asarray(X)
# Then you can simply do
X[s, [0, 1, 2]]
# Or more generally
X_argmax = X[s, numpy.arange(X.shape[1])]
Partial answer: Usesign or signbit.
In [8]: x = numpy.array([-2.1, -6.1, 5])
In [9]: numpy.sign(x)
Out[9]: array([-1., -1., 1.])
In [10]: numpy.signbit(x)
Out[10]: array([ True, True, False], dtype=bool)
