TypeError: Mismatch between array dtype ('object') and format specifier ('%.18e')

Question

I have the following array:

X = np.array([image_array_to_vector1,image_array_to_vector2,image_array_to_vector3,image_array_to_vector4])

A p

Answer 1

In essence savetxt is doing:

for row in your_array:
    print(fmt % tuple(row))

where fmt is constructed your fmt parameter (or the default one) and the number of columns, and the delimiter.

You have a 1d array of objects (arrays). So the write/print will be

 print(fmt % tuple(element))

%s is the only format that can handle an array (or other general object).

savetxt is meant to be used with 2d numeric arrays, the kind of thing that will produce need csv columns. Trying to use it on other things like this object array is going to give you headaches.

In [2]: A = np.empty((3,),dtype=object)
In [3]: A[:] = [np.arange(3),np.arange(1,4), np.arange(-3,0)]
In [4]: A
Out[4]: array([array([0, 1, 2]), array([1, 2, 3]), array([-3, -2, -1])], dtype=object)

In [6]: np.savetxt('test',A,fmt='%s')
In [7]: cat test
[0 1 2]
[1 2 3]
[-3 -2 -1]

Iterating on a 1d array it must be skipping the tuple. In any case the best you can do is a %s format. Otherwise write your own custom file writer. savetxt isn't anything special or powerful.

In [9]: for row in A:
   ...:     print('%s'%row)  
[0 1 2]
[1 2 3]
[-3 -2 -1]