DAX: Mapping items if appeared both in 2 dates - powerbi

Question

How can I map or count new items that were also in my data the previous month?
For example:
ID / date / item
123 / 01.12.20 / one
123 / 01.11.20 / one
143 / 01.11.20 / two
153 / 01.12.20 / three
Will get:
123 / one

Answer 1

It looks like the Item is the description of the ID.
We can write a measure that shows the Item if it was also present in the preious month or blank otherwise. This way, creating a Table visual in Power BI with the ID and this measure we will just see the IDs and Items that where present in the previous month.
Item if in previous month =
IF(
HASONEVALUE( T[Item] )
&& HASONEVALUE( T[ID] ),
VAR currentMonth =
MONTH(
MAX( T[Date] )
)
VAR currentItem =
SELECTEDVALUE( T[Item] )
RETURN
IF(
NOT ISEMPTY(
FILTER(
ALL( T ),
MONTH( T[Date] ) = CurrentMonth - 1
&& T[Item] = currentItem
)
),
currentItem
)
)
This works if we have two months of data, like in your question. If we have more than two months, then maybe that what we really want is to check the previous month of the last one.
Item if in previous to last month =
VAR LastMonth =
MONTH(
MAXX(
ALL( T ),
T[Date]
)
)
RETURN
IF(
HASONEVALUE( T[Item] )
&& HASONEVALUE( T[ID] )
&& MONTH(
MAX( T[Date] )
) = LastMonth,
VAR currentItem =
SELECTEDVALUE( T[Item] )
RETURN
IF(
NOT ISEMPTY(
FILTER(
ALL( T ),
MONTH( T[Date] ) = LastMonth - 1
&& T[Item] = currentItem
)
),
currentItem
)
)