A data analyst is working with a sales dataset in Power Query. The 'SalesAmount' column is currently of type 'Text' and contains values like '1,234.56', '500.00', and occasionally some non-numeric entries like 'N/A' or blank cells. The analyst needs to convert this column to a 'Decimal Number' data type, ensuring that valid numbers are converted correctly and invalid entries are handled gracefully without causing an entire query failure. Which Power Query transformation strategy offers the most robust conversion?
- ARemove Rows with Errors, then Change Type to Decimal Number.
- BAdd a Custom Column using `Number.FromText()` with `try ... otherwise null` logic, then remove original.
- CChange Type to Decimal Number, then use 'Replace Errors' to handle failures.
- DUse 'Replace Values' to convert 'N/A' and blanks to 0, then Change Type to Decimal Number.
Show answer & explanationAnswer & explanation
Correct answer: B. Add a Custom Column using `Number.FromText()` with `try ... otherwise null` logic, then remove original.
Adding a custom column with `try Number.FromText([SalesAmount]) otherwise null` provides the most robust and controlled conversion. It attempts the conversion and, if it fails, gracefully inserts a null, allowing for subsequent handling (e.g., replacing nulls with 0 or filtering them out) without terminating the query.
Why the other options are wrong
- A. Removing rows with errors might discard valid data if only a few cells are problematic. A more graceful handling strategy is usually preferred to preserve as much data as possible.
- C. While 'Replace Errors' can handle failures after 'Change Type', it's a reactive approach. The `try...otherwise` construct is more proactive and allows for more granular error handling decisions.
- D. Replacing specific known non-numeric values like 'N/A' is good, but it might miss other unexpected non-numeric entries. The `try Number.FromText` handles all conversion failures generically.
Robust Numeric Type Conversion (Power Query)
A technique in Power Query, often involving the `try...otherwise` construct with `Number.FromText()`, to convert text to numeric types while gracefully handling non-numeric values by replacing them with nulls or other specified values, preventing query failures.
- Handles varied text formats and non-numeric entries.
- Uses `try ... otherwise` for error resilience.
- Preserves rows instead of generating errors or removing data.
Memory trick: When converting, always 'try' it first, and if it fails, have a 'plan B'.