Detect changed value in a column compared to previous row

[biz_wiz]

Hi,

I need to filter my visual to only show rows where there has been a change in "Attribute" compared to the previous row.

We start with our dataset:

Index	Attribute
1	A
2	A
3	B
4	B
5	C

I imagine the solution would be to build a calculated column with DAX called "Changed". Value 1 for all rows where the there has been a change compared to the previous row, 0 when there has been no change.

Index	Attribute	Changed
1	A	1
2	A	0
3	B	1
4	B	1
5	C	1
6	C	0

Row 1 would ideally also have value 1 as it's the base value and I would like to include in the the visual.

Could somebody point me to the right direction for building th calculated column?

Thank you!

[Anonymous · Accepted solution]

@biz_wiz 

Column = 
VAR _prevattr = CALCULATE(MAX('Table'[Attribute]),FILTER('Table','Table'[Index]<EARLIER('Table'[Index])))
RETURN IF('Table'[Attribute]<>_prevattr,1,0)

Please use this formula to track status change. However one thing I didn't get for index 4 changed value column value is 1 I think it should be 0. Let me know if you have question

[kentyler · Accepted solution]

Thanks for providing a dataset that could be copied and pasted.

Here's the measure I wrote

Changed =

VAR currentIndex =

MAX ( Attributes[Index] )

VAR previousIndex =

IF ( currentIndex = 1, 1, CurrentIndex - 1 )

VAR currentValue =

MAX ( Attributes[Attribute] )

VAR previousValue =

CALCULATE ( MAX ( Attributes[Attribute] ), Attributes[Index] = previousIndex )

RETURN

previousValue = currentValue

The trick to get "previous" values in DAX is to use an idex (which you already had). There is a function named EARLIER, but it does NOT mean the previous row. It refers to the outer filter context and is not appropriate here.

This is a measure, so in several places you cannot just refer to a column directly, but have to wrap your reference in MAX(). The measure will run in a row context, where there will only be one value available. So MAX will return that value.

Here are my results

 

Thanks for posting, it was a fun problem.

Every time I answer a question I learn something

I'm a personal Power BI trainer. 

[Anonymous · Accepted solution]

@biz_wiz 

Column = 
VAR _prevattr = CALCULATE(MAX('Table'[Attribute]),FILTER('Table','Table'[Index]<EARLIER('Table'[Index])))
RETURN IF('Table'[Attribute]<>_prevattr,1,0)

Please use this formula to track status change. However one thing I didn't get for index 4 changed value column value is 1 I think it should be 0. Let me know if you have question