Index all *except* one item in python

by

For a list, you could use a list comp. For example, to make b a copy of a without the 3rd element:

a = range(10)[::-1]                       # [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
b = [x for i,x in enumerate(a) if i!=3]   # [9, 8, 7, 5, 4, 3, 2, 1, 0]

This is very general, and can be used with all iterables, including numpy arrays. If you replace [] with (), b will be an iterator instead of a list.

Or you could do this in-place with pop:

a = range(10)[::-1]     # a = [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
a.pop(3)                # a = [9, 8, 7, 5, 4, 3, 2, 1, 0]

In numpy you could do this with a boolean indexing:

a = np.arange(9, -1, -1)     # a = array([9, 8, 7, 6, 5, 4, 3, 2, 1, 0])
b = a[np.arange(len(a))!=3]  # b = array([9, 8, 7, 5, 4, 3, 2, 1, 0])

which will, in general, be much faster than the list comprehension listed above.

More Related Contents:

  1. How to create a list of list from the given input? [closed]
  2. Replace list object based on indexes of another list (Python)
  3. How do I get the last element of a list?
  4. What are the advantages of NumPy over regular Python lists?
  5. List of lists into numpy array
  6. using an numpy array as indices of the 2nd dim of another array? [duplicate]
  7. How to extract an arbitrary line of values from a numpy array?
  8. Find nearest indices for one array against all values in another array – Python / NumPy
  9. Get the position of the largest value in a multi-dimensional NumPy array
  10. Convert NumPy array to Python list
  11. Explicitly select items from a list or tuple
  12. Why does indexing numpy arrays with brackets and commas differ in behavior?
  13. Tuple unpacking order changes values assigned
  14. Using an index to get an item
  15. Increment Numpy array with repeated indices
  16. Implement list-like index access in Python
  17. Find the index of an item in a list of lists
  18. Find index where elements change value numpy
  19. Numpy individual element access slower than for lists
  20. Indexing a list with an unique index
  21. Python Bool and int comparison and indexing on list with boolean values
  22. Numpy: For every element in one array, find the index in another array
  23. Filtering a list based on a list of booleans
  24. interleaving 2 lists of unequal lengths [duplicate]
  25. Numpy sub-array assignment with advanced, mixed indexing
  26. How to access a column in a list of lists in python
  27. Access n-th dimension in python [duplicate]
  28. numpy array TypeError: only integer scalar arrays can be converted to a scalar index
  29. How can I turn a flat list into a 2D array in python?
  30. Get the indices of N highest values in an ndarray

Leave a Comment