Check if any element of a numpy array is not in a list?

Question

I have a small list:

moveless = [0,11,30,31,20,21,22,23,24,25,26,27,28,29]

And, for example, an array like so (it will always come nested in a list like this, but there will often be tens/hundreds of thousands of them, and any number from -1 to 31 can be in any spot):

starting_board = [([[ 6, -1, -1,  11, 0,  11, -1,  -1,  -1, -1],
       [-1, -1, -1, -1, -1, -1, -1,  11, -1, -1],
       [-1, -1, -1, -1, -1, -1, -1, 1, -1, -1],
       [-1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
       [-1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
       [-1, -1, -1, -1, -1, -1, -1, -1, -1, 2],
       [-1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
       [-1, -1, -1, 20, 31, -1, 25, -1, -1, -1]])]

And I need to determine if any of the elements of this array are not in moveless. So if it parsed it and got to 6, it could stop.

I feel like there must be a faster and more elegant/pythonic way to do this than just a couple for loops, but my checking through the numpy docs/elsewhere on this site hasn't revealed anything terribly useful.

Srce Cde · Accepted Answer · 2018-11-26 15:28:23Z

Using isin()

starting_board = [([[ 6, -1, -1,  11, 0,  11, -1,  -1,  -1, -1],
       [-1, -1, -1, -1, -1, -1, -1,  11, -1, -1],
       [-1, -1, -1, -1, -1, -1, -1, 1, -1, -1],
       [-1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
       [-1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
       [-1, -1, -1, -1, -1, -1, -1, -1, -1, 2],
       [-1, -1, -1, -1, -1, -1, -1, -1, -1, -1],
       [-1, -1, -1, 20, 31, -1, 25, -1, -1, -1]])]
moveless = [0,11,30,31,20,21,22,23,24,25,26,27,28,29]
print(np.isin(starting_board, moveless))

Output:

[[[False False False  True  True  True False False False False]
  [False False False False False False False  True False False]
  [False False False False False False False False False False]
  [False False False False False False False False False False]
  [False False False False False False False False False False]
  [False False False False False False False False False False]
  [False False False False False False False False False False]
  [False False False  True  True False  True False False False]]]

scnerd · Accepted Answer · 2018-11-26 15:29:12Z

1

If all you need to know is if any of the elements are not in the list, just do a set comparison:

any_items_not_in_moveless = {element for row in starting_board[0] for element in row} - set(moveless)
# OR
any_items_not_in_moveless = set(np.asarray(starting_board[0]).ravel()) - set(moveless)

As @Chirag points out, you could also leverage Numpy's isin function. Which solution is faster/better for you is something you'd need to figure out for your own case:

any_items_not_in_moveless = (~np.asarray(starting_board[0]).isin(moveless)).any()

edited Nov 26, 2018 at 15:29

answered Nov 26, 2018 at 15:22

scnerd

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