Fill zero values of 1d numpy array with last non-zero values

by

Here’s a solution using np.maximum.accumulate:

def fill_zeros_with_last(arr):
    prev = np.arange(len(arr))
    prev[arr == 0] = 0
    prev = np.maximum.accumulate(prev)
    return arr[prev]

We construct an array prev which has the same length as arr, and such that prev[i] is the index of the last non-zero entry before the i-th entry of arr. For example, if:

>>> arr = np.array([1, 0, 0, 2, 0, 4, 6, 8, 0, 0, 0, 0, 2])

Then prev looks like:

array([ 0,  0,  0,  3,  3,  5,  6,  7,  7,  7,  7,  7, 12])

Then we just index into arr with prev and we obtain our result. A test:

>>> arr = np.array([1, 0, 0, 2, 0, 4, 6, 8, 0, 0, 0, 0, 2])
>>> fill_zeros_with_last(arr)
array([1, 1, 1, 2, 2, 4, 6, 8, 8, 8, 8, 8, 2])

Note: Be careful to understand what this does when the first entry of your array is zero:

>>> fill_zeros_with_last(np.array([0,0,1,0,0]))
array([0, 0, 1, 1, 1])

More Related Contents:

  1. How to calculate rolling / moving average using python + NumPy / SciPy?
  2. Saving a Numpy array as an image
  3. Intuition and idea behind reshaping 4D array to 2D array in NumPy
  4. Removing nan values from an array
  5. How to count the occurrence of certain item in an ndarray?
  6. How do I compute derivative using Numpy?
  7. binning data in python with scipy/numpy
  8. How do I count the occurrence of a certain item in an ndarray?
  9. Calculating Pearson correlation and significance in Python
  10. ValueError: could not broadcast input array from shape (224,224,3) into shape (224,224)
  11. Sliding window of M-by-N shape numpy.ndarray
  12. numpy array concatenate: “ValueError: all the input arrays must have same number of dimensions”
  13. Precision lost while using read_csv in pandas
  14. How to split a numpy array in fixed size chunks with and without overlap?
  15. Initialise numpy array of unknown length
  16. Saving Matplotlib graphs to image as full screen
  17. Read a base 64 encoded image from memory using OpenCv python library
  18. Pandas in AWS lambda gives numpy error
  19. Pandas groupby with categories with redundant nan
  20. Shuffling NumPy array along a given axis
  21. How to display progress of scipy.optimize function?
  22. Easy way to test if each element in an numpy array lies between two values?
  23. Python numpy: cannot convert datetime64[ns] to datetime64[D] (to use with Numba)
  24. ImportError: No module named numpy on spark workers
  25. sampling random floats on a range in numpy
  26. How does the axis parameter from NumPy work?
  27. How can I draw lines into numpy arrays?
  28. Fast interpolation of grid data
  29. numpy faster than numba and cython , how to improve numba code
  30. Interweaving two NumPy arrays efficiently

Leave a Comment