Finding indices of matches of one array in another array

by

You can use np.in1d with np.nonzero –

np.nonzero(np.in1d(A,B))[0]

You can also use np.searchsorted, if you care about maintaining the order –

np.searchsorted(A,B)

For a generic case, when A & B are unsorted arrays, you can bring in the sorter option in np.searchsorted, like so –

sort_idx = A.argsort()
out = sort_idx[np.searchsorted(A,B,sorter = sort_idx)]

I would add in my favorite broadcasting too in the mix to solve a generic case –

np.nonzero(B[:,None] == A)[1]

Sample run –

In [125]: A
Out[125]: array([ 7,  5,  1,  6, 10,  9,  8])

In [126]: B
Out[126]: array([ 1, 10,  7])

In [127]: sort_idx = A.argsort()

In [128]: sort_idx[np.searchsorted(A,B,sorter = sort_idx)]
Out[128]: array([2, 4, 0])

In [129]: np.nonzero(B[:,None] == A)[1]
Out[129]: array([2, 4, 0])

More Related Contents:

  1. What are the advantages of NumPy over regular Python lists?
  2. ValueError: setting an array element with a sequence
  3. Numpy `logical_or` for more than two arguments
  4. Why are NumPy arrays so fast?
  5. Calculate mean across dimension in a 2D array
  6. How to copy a 2D array into a 3rd dimension, N times?
  7. How do I convert a numpy array to (and display) an image?
  8. How does NumPy’s transpose() method permute the axes of an array?
  9. Numpy random choice to produce a 2D-array with all unique values
  10. How to normalize a NumPy array to within a certain range?
  11. How do I print the full NumPy array, without truncation?
  12. Multiplying across in a numpy array
  13. initialize a numpy array
  14. numpy array assignment problem
  15. Preserve custom attributes when pickling subclass of numpy array
  16. What does dtype=object mean while creating a numpy array?
  17. Python Numpy TypeError: ufunc ‘isfinite’ not supported for the input types
  18. Why is a `for` over a Python list faster than over a Numpy array?
  19. Subtracting numpy arrays of different shape efficiently
  20. Selecting close matches from one array based on another reference array
  21. Repeat each values of an array different times
  22. How to create 2d array with numpy random.choice for every rows?
  23. Input and output numpy arrays to h5py
  24. Why does numpy have a corresponding function for many ndarray methods?
  25. Numpy sub-array assignment with advanced, mixed indexing
  26. Efficiently sorting a numpy array in descending order?
  27. Numpy: Divide each row by a vector element
  28. Setting the fmt option in numpy.savetxt
  29. Access n-th dimension in python [duplicate]
  30. Efficient dot products of large memory-mapped arrays

Leave a Comment