Calculate most recent date

[Daxquest]

Hi,

I have a table of document changes. Each row contains a document id and a time when the change occurred. I need to report on this data in two modes: one that reports on all changes, and another that reports on only the most recent changes for a given document. In order to do this, I think I need a calculated field that shows whether the given row represents the most recent change. As an example, here's what I have:

change_date	document_id
5/1/2015	a
5/1/2015	b
5/1/2015	c
5/1/2015	d
6/20/2015	a
6/20/2015	b
6/20/2015	c
6/20/2015	e
6/20/2015	f
7/11/2015	a
7/11/2015	b
7/11/2015	f
7/11/2015	g

<tbody>
</tbody>

I think what I want is a calculated column that has a 1 if the row is the most recent change, and a 0 if not - then that column can be used as a filter and also to sum and in various other calculations.

My problem is that I can't figure out how to calculate this. My first thought was something like:

=if(
    lastdate( filter( Table, Table[document_id] = [document_id] ) ) = [change_date],
    1, 0
)

But lastdate() wants just a column, not the entire table that filter() spits out. Same with max(). I can't figure out how to narrow down the return of filter() to a single column for the benefit of lastdate(), and I can't figure out an alternative to lastdate() (or max(), which also expects a column) to use instead. Am I missing something? Should I take a different approach?

Many thanks!

 

[Ozeroth]

Here are two ways I can think of. MAX can also be replaced with LASTDATE in this case.

=IF (
     Table[change_date]
        = CALCULATE (
            MAX ( Table[change_date] ),
            ALLEXCEPT ( Table, Table[document_id] )
        ),
    1,
    0
)

=
IF (
    Table[change_date]
        = CALCULATE (
            MAX ( Table[change_date] ),
            FILTER ( Table, Table[document_id] = EARLIER ( Table[document_id] ) )
        ),
    1,
    0
)

 

[Daxquest]

Ozeroth, your name made me chuckle and your solution made me dance. Thanks very much!