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Update README.md

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Signed-off-by: David Rotermund <54365609+davrot@users.noreply.github.com>
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numpy/dimensions/README.md
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@ -8,7 +8,7 @@
## The goal
Matrices have dimensions. But how to add and remove extra dimensions (i.e. dimensions with length 1)?
Questions to [David Rotermund](mailto:davrot@uni-bremen.de)
@ -125,6 +125,12 @@ print(type(data[0:1, 0:1, 0:1])) # -> <class 'numpy.ndarray'>
## Adding dimensions with [np.newaxis](https://numpy.org/doc/stable/reference/constants.html#numpy.newaxis)
```python
numpy.newaxis
```
> A convenient alias for None, useful for indexing arrays.
```python
import numpy as np
@ -139,3 +145,48 @@ print(data[np.newaxis, :, np.newaxis].shape) # -> (1, 2, 1)
print(data[:, np.newaxis, np.newaxis].shape) # -> (2, 1, 1)
```
## Adding dimensions with [numpy.expand_dims](https://numpy.org/doc/stable/reference/generated/numpy.expand_dims.html)
In the case you don’t like newaxis for adding a new dimension...​
```python
numpy.expand_dims(a, axis)
```
> Expand the shape of an array.
>
> Insert a new axis that will appear at the axis position in the expanded array shape.
```python
import numpy as np
data = np.zeros((2))
print(data.shape) # -> (2,)
print(np.expand_dims(data, axis=0).shape) # -> (1, 2)
print(np.expand_dims(data, axis=1).shape) # -> (2, 1)
print(np.expand_dims(data, axis=(1, 2, 3)).shape) # -> (2, 1, 1, 1)
```
## Removing dimensions with [numpy.squeeze](https://numpy.org/doc/stable/reference/generated/numpy.squeeze.html)
```python
numpy.squeeze(a, axis=None)
```
> Remove axes of length one from a.
```python
import numpy as np
data = np.zeros((1, 2, 1, 1))
print(data.shape) # -> (1, 2, 1, 1)
print(np.squeeze(data).shape) # -> (2,)
print(np.squeeze(data, axis=0).shape) # -> (2, 1, 1)
print(np.squeeze(data, axis=2).shape) # -> (1, 2, 1)
print(np.squeeze(data, axis=3).shape) # -> (1, 2, 1)
print(np.squeeze(data, axis=(0, -1)).shape) # -> (2, 1)
print(
np.squeeze(data, axis=1).shape
) # -> ValueError: cannot select an axis to squeeze out which has size not equal to one
```