Finding the index of greatest comparison of elements in a numpy array

Question

I have an array a

and I want to find the position of the largest element in a

that given value is even greater.

In this example:

a = np.array([0, 50, 5, 52, 60])
v = 55

largest element that is v

greater than 52

(index 3), so I want to return 3.

The numpy function argmax()

does not work for this purpose as it returns the first item. What's the quick and correct way to do this with numpy?

+3

jll Apr 30 17 at 14:51

2 answers

You can combine argmax

with where

:

>>> np.nanargmax(np.where(a < v, a, np.nan))
3

np.where

replaces all values above v

with nan

before applying nanargmax

(which is ignored nan

in the calculation):

>>> np.where(a < v, a, np.nan)
array([  0.,  50.,   5.,  52.,  nan])

+3

MSeifert Apr 30 17 at 15:26

user2285236 · Accepted Answer · 2017-04-30T14:56:07+0000

You can slice the array and find the maximum yourself, and then query its index:

np.where(a==a[a<v].max())
Out: (array([3]),)