The following Power BI Report contains seven pages focused on the M functions used in the Get Data and Query Editor experience of Power BI Desktop:
- Function Report: This exposes the M standard library but adds the Function Group and Function Detail columns to make the table easier to filter/browse.
- Function Type Pages: This retrieves the function names and descriptions from the M Reference
- The following categories have dedicated pages: Table, List, Record, Text, Number, Date
Update (4/8): The Table transformation functions are now categorized properly on the Table Functions report page.
A few small tweaks have made recently (e.g. alignment). I’m thinking about a way to expose common function parameters (e.g. JoinKind). A ‘SQL to M’ blog post or two might be useful to follow up this reference report.
Insight Quest 
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