# numpy.isin¶

`numpy.``isin`(element, test_elements, assume_unique=False, invert=False)[源代码]

Calculates element in test_elements, broadcasting over element only. Returns a boolean array of the same shape as element that is True where an element of element is in test_elements and False otherwise.

Parameters: element : array_like Input array. test_elements : array_like The values against which to test each value of element. This argument is flattened if it is an array or array_like. See notes for behavior with non-array-like parameters. assume_unique : bool, optional If True, the input arrays are both assumed to be unique, which can speed up the calculation. Default is False. invert : bool, optional If True, the values in the returned array are inverted, as if calculating element not in test_elements. Default is False. `np.isin(a, b, invert=True)` is equivalent to (but faster than) `np.invert(np.isin(a, b))`. isin : ndarray, bool Has the same shape as element. The values element[isin] are in test_elements.

`in1d`
Flattened version of this function.
`numpy.lib.arraysetops`
Module with a number of other functions for performing set operations on arrays.

Notes

`isin` is an element-wise function version of the python keyword in. `isin(a, b)` is roughly equivalent to `np.array([item in b for item in a])` if a and b are 1-D sequences.

element and test_elements are converted to arrays if they are not already. If test_elements is a set (or other non-sequence collection) it will be converted to an object array with one element, rather than an array of the values contained in test_elements. This is a consequence of the `array` constructor’s way of handling non-sequence collections. Converting the set to a list usually gives the desired behavior.

1.13.0 新版功能.

Examples

```>>> element = 2*np.arange(4).reshape((2, 2))
>>> element
array([[0, 2],
[4, 6]])
>>> test_elements = [1, 2, 4, 8]
array([[ False,  True],
[ True,  False]])
array([2, 4])
```

The indices of the matched values can be obtained with `nonzero`:

```>>> np.nonzero(mask)
(array([0, 1]), array([1, 0]))
```

The test can also be inverted:

```>>> mask = np.isin(element, test_elements, invert=True)
array([[ True, False],
[ False, True]])
array([0, 6])
```

Because of how `array` handles sets, the following does not work as expected:

```>>> test_set = {1, 2, 4, 8}
>>> np.isin(element, test_set)
array([[ False, False],
[ False, False]])
```

Casting the set to a list gives the expected result:

```>>> np.isin(element, list(test_set))
array([[ False,  True],
[ True,  False]])
```