Apply formula to specific numpy array values

Question

I have a 2 dimensional array in numpy and need to apply a mathematical formula just to some values of the array which match certain criteria. This can be made using a for loop and if conditions however I think using numpy where() method works faster.

My code so far is this but it doesn't work

cond2 = np.where((SPN >= -alpha) & (SPN <= 0))
SPN[cond2] = -1*math.cos((SPN[cond2]*math.pi)/(2*alpha))

The values in the orginal array need to be replaced with the corresponding value after applying the formula.

Any ideas of how to make this work? I'm working with big arrays so need and efficient way of doing it. Thanks

Alvaro Fuentes · Accepted Answer · 2014-01-31 16:46:03Z

3

Try this:

cond2 = (SPN >= -alpha) & (SPN <= 0)
SPN[cond2] = -np.cos(SPN[cond2]*np.pi/(2*alpha))

edited Jan 31, 2014 at 16:46

answered Jan 31, 2014 at 16:10

Alvaro Fuentes

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2 Comments

Hooked Over a year ago

Might as well call np.pi as well so everything comes from the same library.

Alvaro Fuentes Over a year ago

@Hooked yes I missed it ... :)

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