Sort the distinct elements of a list in descending order by frequency

APL (14)

{∪⍵[⍒+⌿∘.≡⍨⍵]}

This is a function that takes a list, e.g.:

      names
 John  Doe  Dick  Harry  Harry  Doe  Doe  Harry  Doe  John 
      {∪⍵[⍒+⌿∘.≡⍨⍵]} names
 Doe  Harry  John  Dick

Explanation:

∘.≡⍨⍵: compare each element in the array to each other element in the array, giving a matrix
+⌿: sum the columns of the matrix, giving how many times each element occurs
⍒: give indices of downward sort
⍵[...]: reorder ⍵ by the given indices
∪: get the unique elements

For Python 3:

f=lambda n:sorted(set(n),key=n.count)[::-1]

For Python 2:

f=lambda n:sorted(set(n),cmp,n.count,1)

Demo:

>>> names = ["John","Doe","Dick","Harry","Harry","Doe","Doe","Harry","Doe","John"]
>>> f(names)
['Doe', 'Harry', 'John', 'Dick']

Sort[GatherBy@n][[-1;;1;;-1,1]]

{"Doe", "Harry", "John", "Dick"}

(With n = {"John", "Doe", "Dick", "Harry", "Harry", "Doe", "Doe", "Harry", "Doe", "John"})