Shear a numpy array

Question

I\'d like to \'shear\' a numpy array. I\'m not sure I\'m using the term \'shear\' correctly; by shear, I mean something like:

Shift the first column by 0 places

Answer 1

This can be done using a trick described in this answer by Joe Kington:

from numpy.lib.stride_tricks import as_strided
a = numpy.array([[11, 12, 13],
                 [17, 18, 19],
                 [35, 36, 37]])
shift_axis = 0
increase_axis = 1
b = numpy.vstack((a, a))
strides = list(b.strides)
strides[increase_axis] -= strides[shift_axis]
strides = (b.strides[0], b.strides[1] - b.strides[0])
as_strided(b, shape=b.shape, strides=strides)[a.shape[0]:]
# array([[11, 36, 19],
#        [17, 12, 37],
#        [35, 18, 13]])

To get "clip" instead of "roll", use

b = numpy.vstack((numpy.zeros(a.shape, int), a))

This is probably the most efficient way of doing it, since it does not use any Python loop at all.