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pythonarraysnumpyslice
Daniel F
Daniel F

Reputation: 14399

How to reference a slice/view of a numpy array

An answer I gave earlier raised a question for me: Is it possible to reference a view or slice of a numpy array without repeating a bunch of brackets?

For instance, in the answer I used s=np.argsort(u) and then did all my calculations on a 'virtually' sorted u[s]. I've had situations where I then needed a boolean mask of that array, giving something akin to u[s][mask]. For bigger data I might have a mask of a mask of a mask . . . until things start to look like the end of an episode of Scooby Doo.

But if I assign that array to a variable b=a[s][mask] and change b, a does not change, so I end up carrying a pile of brackets through my calculations. I've tried various arrangements of uv=u.view()[s] but it seems .view() only makes a view of the whole array. Is there another method I am missing?

Upvotes: 4

Views: 943

Answers (1)

John Zwinck
John Zwinck

Reputation: 249462

You may not be able to solve the simple case of u[s] but in more complex cases like u[s][mask] you can:

t = s[mask]
u[t] # same as u[s][mask]

That is, you can simplify your mask to a single variable, but you may not be able to get rid of it completely, unless perhaps you want to write your own wrapper class with __getitem__ and __setitem__.

Upvotes: 2

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