modifying values in numpy array

Question

Let's suppose a and b are given as below:-

a = np.arange(5)
b = [0,1,2]

What I want is that for indices excluding those in b ,values in a should be equal to -1. So in the above case a will be equal to

a = array([0, 1, 2, -1, -1])

There is a method which I am aware of i.e.

a[list(set(a)-set(b))] = -1

but takes too much time, and leads to too much complexity when actually writing the code. As always I am looking out for better methods than the above one. Feel free to use any tools required. Another example (just in case):- if

a = np.arange(12)
b = [3,5,6]

Then what I really want is a = array([-1, -1, -1, 3, -1, 5, 6, -1, -1, -1, -1, -1]) P.S. Don't worry a will always be of the form np.arange(int) and no value of b exceeds the length of a

Dunes · Accepted Answer · 2015-02-28 08:19:35Z

3

Well if the object is to create a range of values that are either the same as their index or -1 then it might be simpler to start with all -1 and add the data you want rather than the other way around.

>>> a = np.full(12, -1, dtype=int)
>>> b = [3, 5, 6]
>>> a[b] = b
>>> a
array([-1, -1, -1,  3, -1,  5,  6, -1, -1, -1, -1, -1])

edited Feb 28, 2015 at 8:19

answered Feb 27, 2015 at 18:32

Dunes

42.1k7 gold badges86 silver badges107 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Ashwini Chaudhary · Accepted Answer · 2015-02-27 17:34:46Z

3

>>> a = np.arange(12)
>>> b = [3,5,6]
>>> a[~np.in1d(np.arange(len(a)), b)] = -1
>>> a
array([-1, -1, -1,  3, -1,  5,  6, -1, -1, -1, -1, -1])

answered Feb 27, 2015 at 17:34

Ashwini Chaudhary

252k60 gold badges478 silver badges519 bronze badges

Collectives™ on Stack Overflow

modifying values in numpy array

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related