Implementing Rank / Partitioned Index

Question

Has anyone implemented a partitioned RANK in Power Query? I understand I can Sort and then create an Index, but how can I define partitions for the index? Is there some way I can make it restart with each new partition value?
For instance, I want to rank company performance in each sport:
let
Source = Table.FromRecords(
{[Company = "Company A", Event = "Swimming", Points = 8],
[Company = "Company A", Event = "Running", Points = 5],
[Company = "Company B", Event = "Swimming", Points = 10],
[Company = "Company B", Event = "Running", Points = 2],
[Company = "Company C", Event = "Swimming", Points = 2],
[Company = "Company C", Event = "Running", Points = 4] })
in
#"Source"
Is there a way to do this, besides manually filtering to a single sport, doing the Sort + Index, repeating this step for each sport, and then appending these steps?

Answer 1

Since there is a built-in rank function in Power Pivot and you have more control over filtering etc., if one has the choice, then Power Pivot is the better option. On the other hand, Curt provides a fine solution if you need to do the equivalent in Power
Query.
It appears though, that you'd rather not have an index column and the lot. An alternative solution involves using a couple of portable custom functions.
ListRankEqual:
(inputValue as any, inputSeries as list, optional orderDescending as nullable logical) as number =>
let
    SortedSeries = if not orderDescending or orderDescending = null then
                    List.Sort(inputSeries,Order.Descending)
                 else
                    List.Sort(inputSeries),
    RankEqual = List.PositionOf(SortedSeries,inputValue)+1
in
    RankEqual
The function has two mandatory parameters and one optional parameter. In your example, inputValue would be the current value in the Points column, specified as [Points] when passed to the function. inputSeries would be the entire Points column, or in this
case, a subset of the Points column. In the body of the function, we sort inputSeries in
descending order to get the rank in ascending order and vice versa.
The second function I call GroupList. I tend to use this function when I want to group a column, but retain the original columns in a table. In your example, we want to rank Swimming and Running independently. Therefore, we need
to create a Swimming points list and a Running points list for the ListRankEqual function.
The code for GroupList:
(keyColumnList as list, keyColumnValue as any, associatedColumnList as list)=>
let
    FilteredKeyColumnPositions = List.PositionOf(keyColumnList, keyColumnValue, Occurrence.All),
    FilteredGroupList = List.Transform(FilteredKeyColumnPositions, each associatedColumnList{_})
in
   FilteredGroupList
keyColumnList is the list of values in the grouping column. In this case, it would be specified as
Source[Event]. keyColumnValue is the current value in the Event column, specified as [Event]. associatedColumnList is the column with the values you want to rank (Source[Points]).
GroupList first finds all the positions of the current value in the Event column. It then uses List.Transform to produce a corresponding Point list. The Swimming event will produce a list containing all of the points for Swimming, and the Running event
will produce a list containing all of the points for Running.
The complete custom formula would be:
ListRankEqual([Points],GroupList(Source[Event],[Event],Source[Points]))
You just toss the formula into a new custom column.