Converting a numpy array of dtype objects to dtype complex

Question

I have a numpy array which I want to convert from an object to complex. If I take that array as dtype string and convert it, there is no problem:

In[22]: bane
Out[22]: array(['1.000027337501943-7.331085223659654E-6j',
       '1.0023086995640738-1.8228368353755985E-4j',
       '-0.017014515914781394-0.2820013864855318j'], 
       dtype='|S41')

In [23]: bane.astype(dtype=complex)
Out[23]: 
array([ 1.00002734 -7.33108522e-06j,  1.00230870 -1.82283684e-04j,
       -0.01701452 -2.82001386e-01j])

But when it is dtype object and I try to convert it, I get an error that a float is required. Why is this?

In [24]: bane.astype(dtype=object)
Out[24]: 
array(['1.000027337501943-7.331085223659654E-6j',
       '1.0023086995640738-1.8228368353755985E-4j',
       '-0.017014515914781394-0.2820013864855318j'], dtype=object)

In [25]: _.astype(dtype=complex)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-25-f5d89c8cc46c> in <module>()
----> 1 _.astype(dtype=complex)

TypeError: a float is required    

To convert it, I use two calls to the astype method which seems clumsy:

bane_obj
Out[27]: 
array(['1.000027337501943-7.331085223659654E-6j',
       '1.0023086995640738-1.8228368353755985E-4j',
       '-0.017014515914781394-0.2820013864855318j'], dtype=object)

In [28]: bane_obj.astype(dtype=str).astype(dtype=complex)
Out[28]: 
array([ 1.00002734 -7.33108522e-06j,  1.00230870 -1.82283684e-04j,
       -0.01701452 -2.82001386e-01j])

Answer 1

I think you might want to do the following, depending on what's inside the object type and if there's no padding to worry about:

bane.view(np.complex64) or
bane.view(np.complex128)

However if that does not work, which it didn't for some small tuple example I tried, the following worked:

bane.astype(np.float).view(np.complex64)

Consider using numpy structures rather than objects for the base dtype, you may have an easier time over all.