how to clear an numpy array by it's elements length

Question

I have a 2 dimensional numpy array:

a=np.array([[1,2,3], 
            [4,5,6,7], 
            [2,3,4]])

How can i efficiently remove the element(row), which contains more than 3 elements(columns), without knowledge about its position?

    a=np.array([[1,2,3], 
                [2,3,4]])

"Remove all rows which are longer than 3."

You don't have a 2D numpy array; they can't vary row lengths like that. You probably have a 1D numpy array with dtype=object. — DSM
– DSM, Commented Jul 9, 2014 at 14:37
thx, but it seems to work ok, so the index to adress elements is kind of the same as in a 2d numpy array? — Flo
– Flo, Commented Jul 9, 2014 at 14:43
If you don't need to do any vector ops, or do any vector slicing. Try a * 2, for example, or a[:,1]. — DSM
– DSM, Commented Jul 9, 2014 at 14:44

Dave · Accepted Answer · 2014-07-09 14:37:02Z

4

This should do the trick (assuming the array is in variable a):

np.array([row for row in a if len(row)<=3])

I use a list comprehension on the numpy array a and only select the elements whose length is three or smaller.

answered Jul 9, 2014 at 14:37

Dave

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