[Numpy-discussion] Nice float -> integer conversion?

Derek Homeier derek@astro.physik.uni-goettingen...
Tue Oct 11 14:06:25 CDT 2011


On 11 Oct 2011, at 20:06, Matthew Brett wrote:

> Have I missed a fast way of doing nice float to integer conversion?
> 
> By nice I mean, rounding to the nearest integer, converting NaN to 0,
> inf, -inf to the max and min of the integer range?  The astype method
> and cast functions don't do what I need here:
> 
> In [40]: np.array([1.6, np.nan, np.inf, -np.inf]).astype(np.int16)
> Out[40]: array([1, 0, 0, 0], dtype=int16)
> 
> In [41]: np.cast[np.int16](np.array([1.6, np.nan, np.inf, -np.inf]))
> Out[41]: array([1, 0, 0, 0], dtype=int16)
> 
> Have I missed something obvious?

np.[a]round comes closer to what you wish (is there consensus 
that NaN should map to 0?), but not quite there, and it's not really 
consistent either!

In [42]: c = np.zeros(4, np.int16)
In [43]: d = np.zeros(4, np.int32)
In [44]: np.around([1.6,np.nan,np.inf,-np.inf], out=c)
Out[44]: array([2, 0, 0, 0], dtype=int16)

In [45]: np.around([1.6,np.nan,np.inf,-np.inf], out=d)
Out[45]: array([          2, -2147483648, -2147483648, -2147483648], dtype=int32)

Perhaps a starting point to harmonise this behaviour and get it closer to 
your expectations (it still would not be really nice having to define the 
output array first, I guess)...

Cheers,
							Derek



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