Miscellaneous

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Miscellaneous

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IEEE 754 floating point special values

Special values defined in numpy: :data:~numpy.nan, :data:~numpy.inf

NaNs can be used as a poor-man's mask (if you don't care what the original value was)

Note: cannot use equality to test NaNs. E.g.: ::

myarr = np.array([1., 0., np.nan, 3.]) np.nonzero(myarr == np.nan) (array([], dtype=int64),)

::

np.nan == np.nan # is always False! Use special numpy functions instead. False

::

myarr[myarr == np.nan] = 0. # doesn't work myarr array([ 1., 0., nan, 3.])

::

myarr[np.isnan(myarr)] = 0. # use this instead find myarr array([1., 0., 0., 3.])

Other related special value functions:

• :func:~numpy.isnan - True if value is nan
• :func:~numpy.isinf - True if value is inf
• :func:~numpy.isfinite - True if not nan or inf
• :func:~numpy.nan_to_num - Map nan to 0, inf to max float, -inf to min float

The following corresponds to the usual functions except that nans are excluded from the results:

• :func:~numpy.nansum
• :func:~numpy.nanmax
• :func:~numpy.nanmin
• :func:~numpy.nanargmax
• :func:~numpy.nanargmin

x = np.arange(10.) x[3] = np.nan x.sum() nan np.nansum(x) 42.0