sage.stats.basic_stats.mode doesn't sort

[schilly]

The sage.stats.basic_stats.mode function claims to sort the result, but it doesn't.

sage: my_list =  [0, 2, 7, 7, 13, 20, 2, 13]
sage: mode(my_list)
[2, 13, 7]

Here is a possible fix by Murray Tannock

def mode(v):
    """
    Return the mode of `v`.  The mode is the sorted list of the most
    frequently occurring elements in `v`.  If `n` is the most times
    that any element occurs in `v`, then the mode is the sorted list
    of elements of `v` that occur `n` times.

    NOTE: The elements of `v` must be hashable and comparable.

    INPUT:

        - `v` -- a list

    OUTPUT:

        - a list

    EXAMPLES::

        sage: v = [1,2,4,1,6,2,6,7,1]
        sage: mode(v)
        [1]
        sage: v.count(1)
        3
        sage: mode([])
        []
        sage: mode([1,2,3,4,5])
        [1, 2, 3, 4, 5]
        sage: mode([0, 2, 7, 7, 13, 20, 2, 13])
        [2, 7, 13]
        sage: mode(['sage', 4, I, 3/5, 'sage', pi])
        ['sage']
        sage: class MyClass:
        ...     def mode(self):
        ...         return [1]
        sage: stats.mode(MyClass())
        [1]
    """
    if hasattr(v,'mode'): return v.mode()
    from operator import itemgetter

    freq = {}
    for i in v:
        if i in freq:
            freq[i] += 1
        else:
            freq[i] = 1

    s = sorted(freq.items(), key=itemgetter(1,0))
    return [i[0] for i in s if i[1] == s[-1][1]]

[chapoton]

New commits:

​85ef664	Mode returns sorted list
​90ec4bb	Merge branch 'mode-fixes' in 8.0.b4

[chapoton]

I made my own branch. This should be an easy review.

---

New commits:

​a24030b

trac 21668 make sure the mode is sorted

[tscrim]

I don't think they necessarily have to be comparable, only to have sorted output. However, this will require catching an exception to return the unsorted list, but that is okay IMO.

[chapoton]

so, is this a positive review, Travis ?

[tscrim]

I would instead say you should do

try:
    return sorted(u for u, f in freq.items() if f == n)
except TypeError:
    return [u for u, f in freq.items() if f == n]

with appropriate changes to the docstring.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​e2fa54a	Merge branch 'u/chapoton/21668' in 8.0.b5
​5755b95	trac 21668 add try except

[chapoton]

Done. But I have no idea what you mean by "appropriate changes".

[tscrim]

We no longer require the elements are comparable and we can say we sort this list if possible.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​1652bef

trac 21668 change in doc

[chapoton]

done

---

New commits:

​1652bef

trac 21668 change in doc

[tscrim]

Thank you.