Saving and loading Python dict with savemat results in error

Framester picture Framester · Feb 10, 2012 · Viewed 29.4k times · Source

Here is an minimal example of the error I get. If I understood the documentation correctly, this should be working, but it seems I did not.

a={}
a['test1']=1
a['test2']=2
a['test3']=3
import scipy.io as io
io.savemat('temp',{'a':a})
b = io.loadmat('temp')
b['a'].keys()

Traceback (most recent call last):
  File "<input>", line 1, in <module>
AttributeError: 'numpy.ndarray' object has no attribute 'keys'

Answer

talonmies picture talonmies · Feb 10, 2012

You seem to be operating under the assumption that scipy.io.savemat is intended to be able to save a standard dictionary. I don't believe that is the case. The dictionary argument holds the names of numpy arrays which are written out into the Matlab file. So you can do something like this

import scipy.io as io
import numpy as np

y1=np.array([1,2,3,4])
y2=np.array([10,20,30,40])
y3=np.array([100,200,300,400])

a={}
a['test1']=y1
a['test2']=y2
a['test3']=y3
io.savemat('temp',a)
b = io.loadmat('temp')

print b['test1']
print b['test2']
print b['test3']

which gives:

[[1]
 [2]
 [3]
 [4]]
[[10]
 [20]
 [30]
 [40]]
[[100]
 [200]
 [300]
 [400]]