Unlocking Insights: Getting the N'th Last Non-Blank Value in DAX
Data analysis in Power BI can often require digging deep into the data to unearth the insights that matter. One common scenario analysts encounter is the need to compute measures based on the N'th last non-blank value in a dataset. This article will walk you through creating a DAX (Data Analysis Expressions) measure that achieves this, ensuring you can accurately pinpoint and analyze these crucial data points in your reports.
Understanding the Challenge
When working with time series data or any dataset that might have gaps (blank values), it's essential to be able to retrieve specific non-blank values, such as the most recent sales figures ignoring any days without sales. This becomes particularly challenging when the data contains irregular gaps.
The DAX Solution
Let's explore a DAX measure designed to calculate an average based on the last three non-blank values in a dataset. This will serve as a practical example of how to address the challenge.
Initial Measure Approach
Non-blank average =
VAR curDate = SELECTEDVALUE(Data[Date], MAX(Data[Date]))
VAR nonBlankTab = FILTER(ALL(Data), NOT(ISBLANK(Data[Amount])) && Data[Date] <= curDate)
VAR rankedTab = FILTER(ADDCOLUMNS(nonBlankTab, "Rank", RANKX(nonBlankTab, [Date])), [Rank] <= 3)
RETURN AVERAGEX(rankedTab, [Amount])
This measure calculates the average for the selected date. If no date context is present, it assumes the latest date. It then filters the table to contain only rows with non-blank sales occurring not later than curDate
. Subsequently, it ranks the dates so that the latest three dates always receive ranks 1, 2, and 3.
Simplified Approach Using TOPN
Non-blank average =
VAR curDate = SELECTEDVALUE(Data[Date], MAX(Data[Date]))
VAR nonBlankTab = FILTER(ALL(Data), NOT(ISBLANK(Data[Amount])) && Data[Date] <= curDate)
VAR rankedTab = TOPN(3, nonBlankTab, [Date])
RETURN AVERAGEX(rankedTab, [Amount])
This version simplifies the measure by leveraging the TOPN
function instead of the ADDCOLUMNS
/RANKX
/FILTER
combo to select the top 3 non-blank records based on the date.
A More Universal Approach
Non-blank average =
VAR curDate = SELECTEDVALUE(Data[Date], MAX(Data[Date]))
VAR nonBlankTab = CALCULATETABLE(FILTER(Data, NOT(ISBLANK(Data[Amount])) && Data[Date] <= curDate), REMOVEFILTERS(Data[Date]))
VAR rankedTab = TOPN(3, nonBlankTab, [Date])
RETURN AVERAGEX(rankedTab, [Amount])
This measure is a more universal version that removes filters from the Date column, making the retrieval of the N'th last non-blank values more flexible and applicable across different scenarios.
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Practical Application and Insight
Implementing such measures can significantly enhance your analytical capabilities within Power BI, allowing for more nuanced and accurate data analysis. By mastering these techniques, you can ensure your reports reflect the real picture, even in datasets with irregular gaps.
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In conclusion, extracting the N'th last non-blank value using DAX in Power BI might present a challenge initially, but with the right approach, it leads to powerful data insights. By following the measure examples and understanding the underlying logic, you can enhance your data analysis capabilities, leading to more informed decision-making.