Shift rows of a numpy array independently

by

Inspired by Roll rows of a matrix independently’s solution, here’s a vectorized one based on np.lib.stride_tricks.as_strided –

from skimage.util.shape import view_as_windows as viewW

def strided_indexing_roll(a, r):
    # Concatenate with sliced to cover all rolls
    p = np.full((a.shape[0],a.shape[1]-1),np.nan)
    a_ext = np.concatenate((p,a,p),axis=1)

    # Get sliding windows; use advanced-indexing to select appropriate ones
    n = a.shape[1]
    return viewW(a_ext,(1,n))[np.arange(len(r)), -r + (n-1),0]

Sample run –

In [76]: a
Out[76]: 
array([[4, 0, 0],
       [1, 2, 3],
       [0, 0, 5]])

In [77]: r
Out[77]: array([ 2,  0, -1])

In [78]: strided_indexing_roll(a, r)
Out[78]: 
array([[nan, nan,  4.],
       [ 1.,  2.,  3.],
       [ 0.,  5., nan]])

More Related Contents:

  1. Convert pandas dataframe to NumPy array
  2. Sorting arrays in NumPy by column
  3. Performance of Pandas apply vs np.vectorize to create new column from existing columns
  4. How to access the ith column of a NumPy multidimensional array?
  5. Python/NumPy first occurrence of subarray
  6. Concatenating two one-dimensional NumPy arrays
  7. Numpy matrix to array
  8. Replacing Numpy elements if condition is met
  9. How to make a multidimension numpy array with a varying row size?
  10. Frequency counts for unique values in a NumPy array
  11. How can I add new dimensions to a Numpy array?
  12. Force NumPy ndarray to take ownership of its memory in Cython
  13. How to normalize a NumPy array to within a certain range?
  14. subsampling every nth entry in a numpy array
  15. How do I create an empty array and then append to it in NumPy?
  16. Immutable numpy array?
  17. How to get a list of all indices of repeated elements in a numpy array
  18. Check if two 3D numpy arrays contain overlapping 2D arrays
  19. Numpy: Creating a complex array from 2 real ones?
  20. Binary random array with a specific proportion of ones?
  21. Add multiple values to one numpy array index
  22. Repeat each values of an array different times
  23. How to create 2d array with numpy random.choice for every rows?
  24. What is the difference between np.array() and np.asarray()?
  25. Flattening a list of NumPy arrays?
  26. Fastest pairwise distance metric in python
  27. Why is Numpy much faster at creating a Zero array compared to replacing the values of an existing array with zeros?
  28. Numpy Vector (N,1) dimension -> (N,) dimension conversion
  29. Add single element to array in numpy
  30. argsort for a multidimensional ndarray

Leave a Comment