Zero-dimensional numpy.ndarray : only element is a 2D array : how to access it?
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Zero-dimensional numpy.ndarray : only element is a 2D array : how to access it?
I have imported a Matlab *.mat file using scipy.io and trying to extract the 2D data from it. There are several arrays inside, and when I am trying to get them I got stuck at the last operation.
The data looks like the image below. When I try to index it: IndexError: too many indices for array
I have googled to the point that it looks like a single valued tuple, where the only element is my array. This in principle must be indexable, but it doesn't work. The type(data) returns <class 'numpy.ndarray'>
So the question is: how do I get my 2D array out of this data structure?
data[0] # Doesn't work.
array[0]
Could you add an example to generate a similar matrix or at least how you are trying to retrieve the data? What does it outputs if you execute
my_array.shape?– Luca Cappelletti
Jul 3 at 8:27
my_array.shape
If I knew how to generate a similar matrix, I would've known the answer. I have found a way around though, some voodoo coding, I will post the reply asap.
– denis
Jul 3 at 8:30
2 Answers
2
A search on loadmat should yield many SO questions that will help you pick apart this result. loadmat has to translate MATLAB objects into Python/numpy approximations.
loadmat
loadmat
data = io.loadmat(filename)
should produce a dictionary with some cover keys and various data keys. list(data.keys()) to identify those.
list(data.keys())
x = data['x']
should match the x variable in the MATLAB workspace. It could be a 2d, order F array, corresponding to a MATLAB matrix.
x
It could be (n,m) object dtype array, corresponding to a MATLAB cell.
It could be a structured array, where the field names correspond to a MATLAB struct attributes.
struct
In your case it looks like you have a 0d object dtype array. The shape is (), an empty tuple (1d has (n,) shape, 2d has (n,m) shape, etc). You can pull the element out of a () array with:
()
y[()]
y.item()
The [()] looks odd, but it's logical. For a 1d array y[1] can be written as y[(1,)]. For 2d, y[1,2] and y[(1,2)] are the same. The indexing tuple should match the number of dimensions. Hence a () can index a () shape array.
[()]
y[1]
y[(1,)]
y[1,2]
y[(1,2)]
()
After some voodoo coding I have found a funny way to solve this:
The initial data is the zero-dimensional where the only element is the 2D array. The way to get this element out apparently is:
z = data.item()[()][0]
print(z)
The final result is below I got my 2D array:
This doesn't work, thank you for your input though.
– denis
Jul 3 at 10:50
Are you telling yourself that your own answer doesn't work?
– hpaulj
Jul 3 at 15:17
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array[0]? Without telling us what you have tried, it's hard to say where your problem might lie.– Zinki
Jul 3 at 8:27