Need to have a rolling count by month

[jvandore]

Hello, I am grateful for ideas/assistance. 

Here is my data

Person	Date	Color	Shade
1	1/01/2017	Blue	Dark
1	3/03/2017	Blue	Pale
1	5/05/2017	Red	None
1	1/01/2018	Blue	Dark
1	4/04/2018	Green	None
2	2/02/2017	Blue	Pale
2	6/06/2017	Blue	Dark
2	10/10/2017	Blue	Pale
2	1/01/2018	Red	Pale

Persons can be Blue, Red or Green. If they are blue, they may be dark blue or pale blue. 

Persons can change over time. In the above example, person 1 starts out as dark blue, changes to pale blue after a few months, then isn't blue for a few months and then is dark blue again. 

I need a chart that looks like this

(I don't need the numbers of the persons in the boxes, I just put those there for clarity.)

I need, for each month, to know how many persons are dark blue and how many are pale blue. 

From our above example, even though there are no rows in the data that explicity refer to 2017-04, we have two pale blue people in 2017-04, because they haven't changed from March 2017 or February 2017 respectively. 

What is the best way in PowerBI to do this sort of chart? Should I make a table in PowerQuery with a row for each month and then do selects to fill in the data in that generated data? 

Or is there a function in PowerBI that does this sort of thing? 

any help will be greatly appreciated. 

[v-juanli-msft]

Best Regards
Maggie

[jvandore · Accepted solution]

actually, this solved my problem. https://community.powerbi.com/t5/Desktop/Looping-in-Power-BI/m-p/137578#M59087

thanks @MarcelBeug !!!