There are 4 ranking methods in FSharp.Stats.Rank:

example = [5,3,3,4,2]

• rankFirst - when ties are present, rank them corresponding to the order of their appearance
  • result :int [] = [5,2,3,4,1]
• rankMin - when ties are present, their rank correspond to the rank of the first occurrence
  • result :float [] = [5,2,2,4,1]
• rankMax - when ties are present, their rank correspond to the rank of the last occurrence
  • result :float [] = [5,3,3,4,1]
• rankAvg - when ties are present, their rank correspond to the average of all tie ranks
  • result :float [] = [5,2.5,2.5,4,1]

1. By now, all functions except rankFirst result in float arrays. The only function where floats can occur is rankAvg. For harmonization I would suggest, that rankFirst as well should report a float array, although it would be a breaking change.

2. There seems to be an issue, that ties are not ranked correct here:

   FSharp.Stats/src/FSharp.Stats/Rank.fs

   Line 65 in 46ab30a

   let minTies a _ = (float a + 1.)

   
   It seems the +1 increment belongs to rankMax rather than rankMin.
   EDIT 01/02/22: THIS WAS A TEMPORAL LOCAL ERROR!

A fix is on the way!