CodyBugstein - 1 year ago 105

Python Question

Can someone explain exactly what the

`axis`

I am terribly confused.

I'm trying to use the function

`myArray.sum(axis=num)`

At first I thought if the array is itself 3 dimensions,

`axis=0`

`axis=1`

However this is not the case, and the documentation does not do a good job helping me out (they use a 3x3x3 array so it's hard to tell what's happening)

Here's what I did:

`>>> e`

array([[[1, 0],

[0, 0]],

[[1, 1],

[1, 0]],

[[1, 0],

[0, 1]]])

>>> e.sum(axis = 0)

array([[3, 1],

[1, 1]])

>>> e.sum(axis=1)

array([[1, 0],

[2, 1],

[1, 1]])

>>> e.sum(axis=2)

array([[1, 0],

[2, 1],

[1, 1]])

>>>

Clearly the result is not intuitive.

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Answer Source

Clearly,

```
e.shape == (3, 2, 2)
```

Sum over an axis is a reduction operation so the specified axis disappears. Hence,

```
e.sum(axis=0).shape == (2, 2)
e.sum(axis=1).shape == (3, 2)
e.sum(axis=2).shape == (3, 2)
```

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