How can you define a custom column in Power BI?

The process of defining a custom column in Power BI is effectively done through Power Query's "Add Column" feature. This feature allows users to manipulate data within their model by creating new columns based on existing ones, applying transformations, or utilizing custom formulas. Power Query provides a user-friendly interface to handle data preparation tasks, making it easy to generate calculated columns that reflect specific business logic or data manipulation needs.

While other methods may touch on aspects of data handling or manipulation, they do not serve the same purpose as the "Add Column" feature. Modifying the data source directly can lead to unintended consequences and may not leverage Power BI's full potential for data transformation. The DAX editor is primarily used for creating measures or calculations in reports rather than adding columns directly to the dataset. Creating a new report from scratch does not inherently involve adding custom columns to existing datasets, as it's more about the presentation rather than the dataset transformation.

Thus, utilizing the "Add Column" feature is not only appropriate but also the most efficient method for defining new columns tailored to specific analytical needs in Power BI.