These references apply to the development of Power Pivot data models in Excel, SSAS Tabular data models, and Power BI data models
From Alberto Ferrari, one of the world’s subject matter experts on the topic of DAX, “7 Reasons DAX is Not Easy“. He says, “DAX is simple, but it is not easy.”
See also my Power BI homepage on this site
Power BI Helper from RADACAD
 Intro to Data Modeling for Power BI |  Introducing DAX |
 Supercharge Power BI – Power BI is Better When You Learn to Write DAX by Matt Allington Click here to buy. |  Collect, Combine, and Transform Data Using Power Query in Excel and Power BI by Gil Raviv |  Exam Ref 70-778, Analyzing and Visualizing Data with Microsoft Power BI by Daniil Maslyuk |  Microsoft SQL Server 2012 Analysis Services – The BISM Tabular Model by Marco Russo, Alberto Ferrari, and Chris Webb |
 The Definitive Guide to DAX – Second Edition by Marco Russo and Alberto Ferrari | FREE! Introducing Microsoft Power BI by Alberto Ferrari and Marco Russo | FREE! Power BI from Rookie to Rock Star by Reza Rad |
DAX Patterns from SQLBI
- A few select references from SQLBI…
- 7 Reasons DAX is Not Easy (“DAX is simple, but it is not easy.”)
- Row Context and Filter Context in DAX
- Understanding Context Transition
- Apply DAX basics in Power BI Desktop from the Power BI documentation, several important subtopics
- Free sample chapter, “Understanding Evaluation Contexts in DAX” from “The Definitive Guide to DAX: Business intelligence with Microsoft Excel, SQL Server Analysis Services, and Power BI” By Alberto Ferrari and Marco Russo