Creating a numpy array fails when I try to create from an array of QString

Question

If the array has a size of 2x2 or greater all is well, but if the dimension of the row is 1, for example 1x2, numpy does something I did not expect.

How can I solve this?

# TEST 1 OK
myarray = np.array([[QString('hello'), QString('world')],
                    [QString('hello'), QString('moon')]],
                   dtype=object)
print myarray
print myarray.shape
#[[PyQt4.QtCore.QString(u'hello') PyQt4.QtCore.QString(u'world')]
# [PyQt4.QtCore.QString(u'hello') PyQt4.QtCore.QString(u'moon')]]
#(2, 2)


# TEST 2 OK
myarray = np.array([['hello'], ['world']], dtype=object)
print myarray
print myarray.shape  
#[['hello']
# ['world']]
#(2, 1)


# TEST 3 FAIL
myarray = np.array([[QString('hello'), QString('world')]], dtype=object)
print myarray
print myarray.shape
#[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[PyQt4.QtCore.QString(u'h')]]]]]]]]]]]]]]]]]]]]]]]]]]]]]
#..
#[[[[[[[[[[[[[[[[[[[[[[[[[[[[[PyQt4.QtCore.QString(u'e')]]]]]]]]]]]]]]]]]]]]]]]]]]]]]
# etc...
#(1, 2, 5, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1)

Oh weird... Almost seems like numpy is treating the strings as arrays or something... What happens if you put a comma between the 2 closing square brackets? — karina
– karina, Commented Apr 29, 2016 at 7:10

Community · Accepted Answer · 2017-05-23 12:07:43Z

2

Try different length strings:

np.array([[QString('hello'), QString('moon')]], dtype=object)`.

or the create and fill approach to making an object array

A = np.empty((1,2), dtype=object)
A[:] = [QString('hello'), QString('moon')]

I'm not familiar with these objects, but in other cases where we try to build object arrays from lists, it is tricky if the lists are the same length. If QString is iterable, with a .__len__ something similar may be happening.

I'm guessing your first example works because on QString is shorter than the others, not because it is 2x2.

This recent question about making an object array from a custom dictionary class may be relevant: Override a dict with numpy support

edited May 23, 2017 at 12:07

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answered Apr 29, 2016 at 7:45

hpaulj

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1 Comment

David Miró Over a year ago

It is true, I tried the first example and fails if the lengths are identicals!. Good link, maybe the cause of the problem it's related with stackoverflow.com/a/36666424/2270217 , but I think that your solution for me it's enough Thank you!

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