Following piece of code was working in numpy 1.7.1 but it is giving value error in the current version. I want to know the root cause of it.
import numpy as np x = [1,2,3,4] y = [[1, 2],[2, 3], [1, 2],[2, 3]] a = np.array([x, np.array(y)])
Following is the output I get in numpy 1.7.1
>>>a array([[1, 2, 3, 4], [array([1, 2]), array([2, 3]), array([1, 2]), array([2, 3])]], dtype=object)
But the same code produces error in version 1.9.2.
----> 5 a = np.array([x, np.array(y)]) ValueError: could not broadcast input array from shape (4,2) into shape (4)
I have found one possible solution the this. But I don't know whether this is the best thing to do.
b= np.empty(2, dtype=object) b[:] = [x, np.array(y)] >>> b array([[1, 2, 3, 4], array([[1, 2], [2, 3], [1, 2], [2, 3]])], dtype=object)
Please suggest a solution to achieve the desired output. Thanks
What exactly are you trying to produce? I don't have a 1.7 version to test your example.
np.array(x) produces a (4,) array. np.array(y) a (4,2).
As noted in a comment, in 1.8.1 np.array([x, np.array(y)]) produces
ValueError: setting an array element with a sequence.
I can make a object dtype array, consisting of the list and the array
In [90]: np.array([x, np.array(y)],dtype=object) Out[90]: array([[1, 2, 3, 4], [array([1, 2]), array([2, 3]), array([1, 2]), array([2, 3])]], dtype=object)
I can also concatenate 2 arrays to make a (4,3) array (x is the first column)
In [92]: np.concatenate([np.array(x)[:,None],np.array(y)],axis=1) Out[92]: array([[1, 1, 2], [2, 2, 3], [3, 1, 2], [4, 2, 3]])
np.column_stack([x,y]) does the same thing.
Curiously in a dev 1.9 (I don't have production 1.9.2 installed) it works (sort of)
In [9]: np.__version__ Out[9]: '1.9.0.dev-Unknown' In [10]: np.array([x,np.array(y)]) Out[10]: array([[ 1, 2, 3, 4], [174420780, 175084380, 16777603, 0]]) In [11]: np.array([x,np.array(y)],dtype=object) Out[11]: array([[1, 2, 3, 4], [None, None, None, None]], dtype=object) In [16]: np.array([x,y],dtype=object) Out[16]: array([[1, 2, 3, 4], [[1, 2], [2, 3], [1, 2], [2, 3]]], dtype=object)
So it looks like there is some sort of development going on.
In any case making a new array from this list and a 2d array is ambiguous. Use column_stack (assuming you want a 2d int array).
numpy 1.9.0 release notes:
The performance of converting lists containing arrays to arrays using np.array has been improved. It is now equivalent in speed to np.vstack(list).
With transposed y vstack works:
In [125]: np.vstack([[1,2,3,4],np.array([[1,2],[2,3],[1,2],[2,3]]).T]) Out[125]: array([[1, 2, 3, 4], [1, 2, 1, 2], [2, 3, 2, 3]])
If 1.7.1 worked, and x was string names, not just ints as in your example, then it probably was producing a object array.
