NaN is designed to propagate through all calculations, infecting them like a virus, so if somewhere in your deep, complex calculations you hit upon a NaN, you don't bubble out a seemingly sensible answer. Otherwise by identity NaN/NaN should equal 1, along with all the other consequences like (NaN/NaN)==1, (NaN*1)==NaN, etc.

2013年7月25日 · NaN preserving and NA preserving work "equivalently" in R, so if you agree that NA^0 should give 1, NaN^0 |-> 1 is a consequence. Indeed (as others said) you should really read R's help pages and not C or IEEE standards, to answer …

2019年1月20日 · I have z = np.array([4.4, 3, 0, np.nan, -1, 6]) and just can't find any quick and friendly solution for easy replacement. I can't believe it's sometimes such not user friendly language. I tried: np.where(z == np.nan, -1, z) nothing happens. np.nan_to_num(z, -1) changes to zeros. z = [-1 if np.nan(x) else x for x in z] TypeError: 'float' object ...

2018年3月29日 · Type Result Null +0 Undefined NaN And NaN + anything is NaN. This might make some sense from the language perspective: null means an explicit empty value whereas undefined implies an unknown value. In some way - zero is the "number empty value" since it is neutral to addition.

2011年1月6日 · 1#QNAN is a string representation for a "quiet NAN". A "NAN" is "not-a-number" and applies only to floats and doubles. NANs can be very useful actually for representing "null" values (rather than picking some genuine number and hoping for the best you don't need that number for its natural meaning).

2009年12月18日 · NAN may or may not be defined, and "is defined if and only if the implementation supports quiet NaNs for the float type. It expands to a constant expression of type float representing a quiet NaN." Note that if you're comparing floating point values, and do: a = NAN; even then, a == NAN; is false. One way to check for NaN would be:

2013年7月24日 · Different operating systems and programming languages may have different string representations of NaN: nan NaN NaN% NAN NaNQ NaNS qNaN sNaN 1.#SNAN 1.#QNAN -1.#IND I think having all three is just a convenience. They are the same. >>> np.nan nan >>> np.NaN nan >>> np.NAN nan >>>

2015年3月23日 · A NaN can only have three origins in your code: mean is a NaN. In std/=(count); if count is 0. In std=sqrt(std); if std at this point is a negative number (seems impossible in your case). You should debug your code and watch count …

2013年12月2日 · No, as I said in the original question, nans aren't unique objects. Look at the above transcript: the two nans have different ids and nans[0] is nans[1] is False. nan in [nan] is True because it's basically any(x is nan or x == nan for x in [nan]). x is nan is True so it doesn't matter that x == nan is False.

2015年1月20日 · Present in the legacy GAC, c:\windows\assembly, it also has the 10.1.0.0 version. There is a DLL Hell story here, the 10.1.0.0 version was the one used in VS2010. It had the bug, not properly checking for Double.NaN. Microsoft made a mistake, they fixed 10.1.0.0 but did not change the version number.