newaxis.Rmd

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---

# Adding length 1 dimensions with newaxis

NumPy has a nice shortcut for adding a length 1 dimension to an array.  It is
a little brain-bending, because it operates via array slicing:

```{python}
import numpy as np
```

```{python}
v = np.array([0, 3])
v.shape
```

```{python}
# Insert a new length 1 dimension at the beginning
row_v = v[np.newaxis, :]
print(row_v.shape)
row_v
```

```{python}
# Insert a new length 1 dimension at the end
col_v = v[:, np.newaxis]
print(col_v.shape)
col_v
```

Read this last slicing operation as “do slicing as normal, except, before
slicing, insert a length 1 dimension at the position of `np.newaxis`”.

In fact the name `np.newaxis` points to the familiar Python `None` object:

```{python}
np.newaxis is None
```

So, you also use the `np.newaxis` trick like this:

```{python}
row_v = v[None, :]
row_v.shape
```