How does filtering column by itself work?

[mariogmgi2g]

Hi guys,

I have table with a column that look like this:

'A'[Dates] = [10/2/2021, 10/2/2021, 10/2/2021, 11/2/2021, 12/2/2021, 12/2/2021]

and I want to create a knew column to count hoy many times each date appear. 

I thought I could achieve that with the next sentence:
CALCULATE(COUNTROWS(FILTER('A', 'A'[Dates] = 'A'[Dates])))

So, each time the function will be evaluated in each row, count the number of rows that have the same date. This is not working and i would like to know why to understand more precisely this kind of DAX functions.

Thank you very much.

[mariogmgi2g]

@amitchandak Thank you so much for the quick answer! It works perfectly

[amitchandak · Accepted solution]

@mariogmgi2g , a new column =

countx(filter('A', 'A'[Dates] = earlier('A'[Dates])),'A'[Dates] )

or a new measure
countx(filter(allselected('A'), 'A'[Dates] = max('A'[Dates])),'A'[Dates] )