[Numpy-discussion] getting the equivalent complex dtype from a real or int array

Sebastian Berg sebastian at sipsolutions.net
Tue Oct 29 14:01:05 EDT 2013

On Tue, 2013-10-29 at 16:47 +0000, Henry Gomersall wrote:
> Is there a way to extract the size of array that would be created by 
> doing 1j*array?

There is np.result_type. It does the handling of scalars as normal,
dtypes will be handled like arrays (scalars are allowed to lose

- Sebastian

> The problem I'm having is in creating an empty array to fill with 
> complex values without knowing a priori what the input data type is.
> For example, I have a real or int array `a`.
> I want to create an array `b` which can hold values from 1j*a in such a 
> way that I don't need to compute those explicitly (because I only need 
> parts of the array say), without upcasting (or indeed downcasting) the 
> result.
> So if `a` was dtype 'float32`, `b` would be of dtype `complex64`. If `a` 
> was `int64`, `b` would be of dtype `complex128` etc.
> Cheers,
> Henry
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