comparing_arrays.Rmd

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## Comparing arrays

A comparison between two arrays returns the *elementwise* result of the
comparison:

```{python}
import numpy as np
arr1 = np.array([[0, 1, 2],
                [3, 4, 5]])
arr2 = np.array([[1, 1, 2],
                 [3, 4, 6]])
arr1 == arr2
```

Sometimes we want to know if two arrays are equal, in the sense that all the
elements of the two arrays are equal to each other. For this we use
`np.all`. `np.all` accepts an array as input, and returns True if all the
elements are non-zero .

```{python}
np.all([1, 2, 3])
```

Python assumes that `True == 1` and `False == 0` for this test of
non-zero:

```{python}
np.all([True, True, True])
```

```{python}
np.all([1, 2, 0])
np.all([True, False, True])
```

To ask whether all the elements in two arrays are equal, we can pass the
result of the element-wise comparison to `np.all`:

```{python}
np.all(arr1 == arr2)
```

```{python}
arr3 = arr1.copy()
np.all(arr1 == arr3)
```

Sometimes we want to know if any of the values in an array are non-zero
.  Enter `np.any`:

```{python}
np.any([False, False, False])
```

```{python}
np.any([False, False, True])
```

```{python}
np.any(arr1 == arr2)
```

```{python}
np.any(arr1 != arr3)
```

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