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Clarify floating-point sort order for ascending and descending sort #288
Description
Currently, the specification does not indicate the behavior for sorting the IEEE 754 floating-point values: NaN, -0, and +0.
In NumPy, NaN values are sorted to the end and signed zeros are not sorted:
In [1]: np.sort([2.0, 0.0, 1.0, -0.0, np.nan, np.nan, 3.0])
Out[1]: array([ 0., -0., 1., 2., 3., nan, nan])When sorting lists in Python, NaN values are left in place and signed zeros are not sorted:
In [1]: list = [2.0,0.0,1.0,-0.0,float('nan'),float('nan'),3.0,-1.0];
In [2]: list.sort()
In [3]: list
Out[3]: [-1.0, 0.0, -0.0, 1.0, 2.0, nan, nan, 3.0]Other languages have made different design decisions. E.g., Julia sorts signed zeros and places NaN values at the end.
julia> sort([2.0,1.0,0.0,-0.0,NaN,NaN,3.0,-1.0])
8-element Array{Float64,1}:
-1.0
-0.0
0.0
1.0
2.0
3.0
NaN
NaNIMO, we should clarify the sort order for ascending and descending sort. Preferably,
- sorting signed zeros
- sorting
NaNvalues to the end when sorting in ascending order and to the beginning when sorting in descending order
Activity
kgryte commentedon Oct 21, 2021
By specifying sort order for floating-point values, this has implications for
unique(see gh-249), as sortingNaNvalues to the ends affords relatively straightforward workarounds for handling multiple returnedNaNs as discussed in the referenced issue.