How do I convert a NumPy array to a Python List (for example `[[1,2,3],[4,5,6]]`

), and do it reasonably fast?

Use `tolist()`

:

```
import numpy as np
>>> np.array([[1,2,3],[4,5,6]]).tolist()
[[1, 2, 3], [4, 5, 6]]
```

Note that this converts the values from whatever numpy type they may have (e.g. np.int32 or np.float32) to the “nearest compatible Python type” (in a list). If you want to preserve the numpy data types, you could call list() on your array instead, and you’ll end up with a list of numpy scalars. (Thanks to Mr_and_Mrs_D for pointing that out in a comment.)

NumPy arrays have a tolist method:

```
In [1]: arr=np.array([[1,2,3],[4,5,6]])
In [2]: arr.tolist()
Out[2]: [[1, 2, 3], [4, 5, 6]]
```

The numpy .tolist method produces nested arrays if the numpy array shape is 2D.

if flat lists are desired, the method below works.

```
import numpy as np
from itertools import chain
a = [1,2,3,4,5,6,7,8,9]
print type(a), len(a), a
npa = np.asarray(a)
print type(npa), npa.shape, "\n", npa
npa = npa.reshape((3, 3))
print type(npa), npa.shape, "\n", npa
a = list(chain.from_iterable(npa))
print type(a), len(a), a`
```

If you have a ndarray in numpy called narray

Example

```
narray[0] = [[[ 87 137]] [[ 87 138]] [[ 86 139]][[ 85 140]][[ 85 141]]]
narray[1] = [[[ 84 142]] [[ 84 143]] [[ 83 144]]]
narray[2] = [[[ 82 145]] [[ 81 146]] [[ 80 147]] [[ 79 148]] [[ 78 149]] [[ 77 150]][[ 77 151]]]
```

You could just loop inside a loop like to extra each element separately

```
for i in range(len(narray)):
i_narray = narray[i]
for j in range(len(i_narray)):
print(i_narray[j],"\n")
```

This is the output

```
[[ 87 137]]
[[ 87 138]]
[[ 86 139]]
[[ 85 140]]
[[ 85 141]]
[[ 84 142]]
[[ 84 143]]
[[ 83 144]]
[[ 82 145]]
[[ 81 146]]
[[ 80 147]]
[[ 79 148]]
[[ 78 149]]
[[ 77 150]]
[[ 77 151]]
```

Hope it helps someone 🙂

Tags: laravelpython, list, numpy, struct