Ranking of numpy array with possible duplicates

Question

I have a numpy array of floats/ints and want to map its elements into their ranks.

If an array doesn\'t have duplicates the problem can be solved by the following co

Answer 1

Here is a function that can return the output you desire (in the first case)

def argsortdup(a1):
  sorted = sort(a1)
  ranked = []
  for item in a1:
    ranked.append(sorted.searchsorted(item))
  return array(ranked)

Basically you sort it and then you search for the index the item is at. Assuming duplicates the first instance index should be returned. I tested it with your a2 example and doing something like

a3 = argsortdup(a2)

Yields

array([0, 1, 4, 5, 6, 1, 7, 8, 8, 1])

"Test with a2":

>>> a2
array([ 0.1,  1.1,  2.1,  3.1,  4.1,  1.1,  6.1,  7.1,  7.1,  1.1])
>>> def argsortdup(a1):
...   sorted = sort(a1)
...   ranked = []
...   for item in a1:
...     ranked.append(sorted.searchsorted(item))
...   return array(ranked)
...
>>> a3 = argsortdup(a2)
>>> a2
array([ 0.1,  1.1,  2.1,  3.1,  4.1,  1.1,  6.1,  7.1,  7.1,  1.1])
>>> a3
array([0, 1, 4, 5, 6, 1, 7, 8, 8, 1])
>>>