DATEDIFF between 2 rows aggregating by 2 columns DAX - powerbi

Question

I have a big data set with the structure as shown below.
Operation
User
Timestamp
Elapsed time
12
1
2018-01-03
11:19:02 AM
12
1
2018-01-03
12:34:02 PM
12
1
2018-01-04
8:34:02 AM
12
2
2018-02-03
9:34:02 AM
12
2
2018-02-03
11:12:42 AM
12
3
2018-02-03
12:12:00 PM
15
1
2018-01-02
9:22:32 AM
15
1
2018-01-02
9:25:32 AM
15
2
2018-01-02
9:25:32 AM
The goal is to form the column "Elapsed Time" using DAX and PowerBI. The column shows the difference/duration between the current timestamp and previous timestamp for the same user and the same operation.
I've tried something along the lines of:
Elapsed time =
DATEDIFF (
CALCULATE (
MAX ( data[Timestamp] ),
ALLEXCEPT ( data, data[Operation], data[User] ),
data[Timestamp] < EARLIER ( data[Timestamp] )
),
data[Timestamp],
MINUTE
)
`
But it complains about a single value for column 'Timestamp' in table 'data' cannot be determined. this can happen when a measure formula refers to a column that contains many values without specifying an aggregator such as min, max, count, or sum to get a single result.
I'm very new to DAX, so I'd appreciate any help.

Answer 1

Since the 'Table'[Operation] and 'Table'[User] of the current row are to be used as filter, a very simple approach might just use CALCULATE to trigger the context transition, transforming the current row context to the corresponding filter context, and then to replace the filer over 'Table'[Timestamp] to be less than the current Timestamp, previously saved to a variable. The context transition automatically sets the correct filters over 'Table'[Operation] and 'Table'[User]
Elapsed time =
VAR CurrentTimestamp = 'Table'[TimeStamp]
RETURN
DATEDIFF (
CALCULATE ( MAX ( 'Table'[Timestamp] ), 'Table'[Timestamp] < CurrentTimestamp ),
CurrentTimestamp,
MINUTE
)

Answer 2

Typing on the mobile, so apologies for possible errors. Assuming this is a calculated column:
Elapsed time =
DATEDIFF (
CALCULATE (
MAX ( Table[Timestamp] ),
FILTER (
Table,
Table[User] = EARLIER ( Table[User] )
&& Table[Operation] = EARLIER ( Table[Operation] )
&& Table[Timestamp] < EARLIER ( Table[Timestamp] )
)
),
Table[Timestamp],
MINUTE
)
Where Table is your table name.
There surely are now ways to do that, do apologies for non optimal approach.