Checking existence of an array inside an array of arrays python [duplicate]

Question

I have a numpy array of arrays:

qv=array([[-1.075, -1.075, -3.   ],
       [-1.05 , -1.075, -3.   ],
       [-1.025, -1.075, -3.   ],
       ..., 
       [-0.975, -0.925, -2.   ],
       [-0.95 , -0.925, -2.   ],
       [-0.925, -0.925, -2.   ]])

And I want to determine if an array is contained in that 2-D array and return its index.

qt=array([-1.  , -1.05, -3.  ])

I can convert both arrays to lists and use the list.index() function:

qlist=qv.tolist()
ql=qt.tolist()
qindex=qlist.index(ql)

But I would like to avoid doing this because I think it will be a performance hit.

I will. Once it becomes clear how to do it using numpy instead of lists. — Jen
– Jen, Commented May 6, 2013 at 23:29

Bi Rico · Accepted Answer · 2013-05-06 23:30:58Z

3

This should do the trick,

import numpy as np
np.where((qv == qt).all(-1))

Or

import numpy as np
tol = 1e-8
diff = (qv - qt)
np.where((abs(diff) < tol).all(-1))

The second method might be more appropriate when floating point precision issues come into play. Also, there might be a better approach if you have many qt to test against. For example scipy.spatial.KDTree.

answered May 6, 2013 at 23:30

Bi Rico

25.9k3 gold badges57 silver badges75 bronze badges

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

1 Comment

Jen Over a year ago

Hooray! +1 for floating point considerations. For my particular test set, %timeit in ipython shows that your method is 30.5 ns, vs 770 us for the list method. Thanks!

Collectives™ on Stack Overflow

Checking existence of an array inside an array of arrays python [duplicate]

1 Answer 1

1 Comment

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Linked

Related