Daily DAX : Day 189 LASTNONBLANK

 The LASTNONBLANK function in Power BI's DAX (Data Analysis Expressions) language is used to retrieve the last non-blank value in a column, based on the sort order of another column (typically a date or time column). It is particularly useful for scenarios where you need to identify the most recent non-empty value in a dataset, such as in time-based or sequential data analysis.

Syntax

DAX

LASTNONBLANK(<column>, <expression>)

    <column>: The column to search for the last non-blank value.

    <expression>: An expression that defines the values to evaluate for non-blankness. This is typically a measure or a column reference.

How It Works

    The function scans the specified <column> in the order defined by the current filter context (often a date or another sequential column).

    It returns the last value in <column> where the corresponding <expression> is non-blank (i.e., not empty, null, or blank).

    The sort order is determined by the filter context, so you often pair it with a date or index column to define "last."

Use Case

Scenario: You have a sales dataset with dates and sales amounts, but some dates have missing sales data (blank or null). You want to find the most recent sales amount that is not blank.

Example:

Suppose you have a table Sales:

Date                SalesAmount

2023-01-01        100

2023-01-02        

2023-01-03         200

2023-01-04

You want to find the last non-blank sales amount.

DAX Formula:

DAX

LastSale = LASTNONBLANK(Sales[Date], Sales[SalesAmount])

Result:

    The function evaluates Sales[SalesAmount] in the context of Sales[Date] (sorted ascending).

    It skips blank values (e.g., 2023-01-02 and 2023-01-04) and returns the last non-blank value, which is 200 (corresponding to 2023-01-03).

Practical Use Cases

    Inventory Management: Find the last recorded stock level for a product before the current date.

    Financial Reporting: Retrieve the most recent non-blank value for a financial metric, like revenue or profit, in a time series.

    Customer Activity: Identify the last non-blank purchase amount or activity date for a customer.

    Data Cleaning: Handle sparse datasets by focusing on the most recent valid (non-blank) data points.

Key Notes

    Filter Context: Ensure the correct filter context is applied (e.g., sorting by date). Use CALCULATE or FILTER if needed to enforce specific sorting or filtering.

    Performance: LASTNONBLANK is optimized for time intelligence scenarios but can be resource-intensive with large datasets. Ensure proper indexing on the sorting column (e.g., Date).

    Alternative: Compare with LASTDATE (for dates) or MAX (for numeric values) if non-blank values are not the primary concern.

Example with CALCULATE

To ensure the function respects a specific date range:

DAX

LastSaleIn2023 = 

CALCULATE(

    LASTNONBLANK(Sales[Date], Sales[SalesAmount]),

    Sales[Date] <= DATE(2023, 12, 31)

)

This retrieves the last non-blank sales amount before the end of 2023.

In summary, LASTNONBLANK is a powerful function for time-based or sequential analysis, enabling you to focus on the most recent valid data point in a dataset while ignoring blanks.