Delete from numpy arrays

Question

I have two arrays in NumPy

a = np.array([])
b = np.array([])

These arrays are being populated throughout the code with cohesive values. But now I want to delete elements from both arrays where values in a are greater than the number 5.

I guess it's something like

a = a[~a>5]

but I don't know how to delete the element with exact same index in the array b.

you can set an index ix = a <= 5 and then a = a[ix] and b = b[ix] (or do it in one line a = a[a <= 5] — paddyg
– paddyg, Commented May 8, 2015 at 7:38

Kasravnd · Accepted Answer · 2015-05-08 07:40:54Z

1

You can use np.extract to select the specific elements and reassigned to your array again :

>>> x = np.arange(10)
>>> x=np.extract(x<5,x)
>>> x
array([0, 1, 2, 3, 4])

numpy.extract(condition, arr)

Return the elements of an array that satisfy some condition.

You can also use indexing for such task :

>>> x = np.array([3,4,7,11,0,34,6,1,3,4,2])
>>> x[x<5]
array([3, 4, 0, 1, 3, 4, 2])
>>> np.extract(x<5,x)
array([3, 4, 0, 1, 3, 4, 2])

edited May 8, 2015 at 7:40

answered May 8, 2015 at 7:35

Kasravnd

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