Intro to DAX Patterns

 Eric Bragas – MCP, PSM I
 DesignMind - Business Intelligence Consultant

Agenda
 DAX
 Data Analysis Expressions
 Notation
 Functions
 Evaluation Contexts
 Measure Patterns
 Calculated Column Patterns

Data Analysis Expressions (DAX)
 What is DAX?
 DAX is a language that allows us to write dynamic expressions for relataional
constructs, using familiar functions
 Powerful dynamic data analysis tool for relational data
 Expressions can traverse relationships!
 Available in PowerPivot, PowerBI, and SSAS Tabular
 Classic “Import Mode”
 What isn’t DAX?
 NOT a programming language

DAX Notation
Table
‘Table’
Column
‘Table’[Column]
Function
fn ( <arguments> )
Measure
Measure Name := SUM ( ‘Table’[Column] )
Calculated Column
Column Name = SUM ( ‘Table’[Column] )

Measures
 A measure is a formula/expression comprising functions applied to
columns and tables
 Reusable aggregation evaluated differently, depending on how you use it
 Measures can be nested

Functions
 Logical
 IF( logical test, <value if true>, <value if false> )
 SWITCH( <expression>, <value>, <result>, … ) – evaluates an expression against a list of values, and returns the result corresponding to the first matching value
 TRUE() – returns logical true
 Aggregate
 SUM( <column> ) – adds all the numbers in a column
 DIVIDE( <numerator>, <denominator>, [, <alternateresult>] ) – basic division; optional value returned
 Statistical
 MAX( <column> ) – returns the largest numeric value in a <column>
 MIN( <column> ) – returns the smallest value in a <column>
 Text
 BLANK() – returns a blank
 Filter
 FILTER(<table>, <filter>) – returns a table representing a subset of another table or expression
 ALL( <table> | <column>) – returns all the rows in a table, ignoring any filter context
 VALUES(<table or column>) – returns one column of the distinct values from the specified column or table
 CALCULATE( <expression>, <filter1>, <filter2>, … ) – evaluates an expression in a context that is modified by the specified filters

Functions (cont’d)
 Date and Time
 TODAY() – returns the current date
 NOW() – returns the current date and time in datetime format
 Time Intelligence*
 DATESBETWEEN(<dates>, <start date>, <end date>) – returns a table of <dates> starting with the <start date> and continues
until the <end date>.
 NEXTDAY(<dates>) – returns a table that contains a column with the next dates following each of the <dates> passed
 FIRSTDATE(<dates>) – returns the first date in the context of the specified column of dates
 LASTDATE(<dates>) – returns the last date in the context of the specified column of dates
 SAMEPERIODLASTYEAR(<dates>) – returns a table with a column of dates shifted one year back for each of the <dates> specified
 LASTNONBLANK( <column>, <expression> ) – returns last value in the <column> where the <expression> returns blank
 FIRSTNONBLANK( <column>, <expression> ) – returns the first value in the <column> where the <expression> returns blank
*Requires Date Table

Evaluation Contexts
 Evaluation Contexts:
 Filter Context
 Four types of filter context:
1. Row Selection
2. Column Selection
3. Slicer Selection
4. Filter Selection
 Defines the subset of data a measure is calculated using aka “Which rows are selected based on which attribute
values?”
 Applied before anything else
 Row Context
 All the columns in the Current Row
“DAX is simple, it’s not easy, but it’s
simple”
- Alberto Ferrari

Basic Evaluation Context - Demo
TotalSales = SUM ( Sales[SalesAmount] )

Anatomy of a Filter Context -
PivotTable
Rows
Slicer

Anatomy of a Filter Context - Chart
Filter
Slicer

Measure Patterns
BASIC
CUMULATIVE
YTD
YEAR OVER YEAR
SEMI-ADDITIVE
DISCONNECTED SLICERS

Basic Measures
 SUM( ‘Sales’[SalesAmount] )
 AVERAGE( ‘Inventory’[InventoryOnHand] )
 MIN( ‘Weather’[Temp] )
 MAX ( ‘Weather’[Temp] )
 Etc.

Basic Measure Demo – PowerPivot &
PowerBI
Asia Sales :=
CALCULATE ( [Total Sales],
Geography[ContinentName] = "Asia" )
Asia Sales :=
CALCULATE (
[Total Sales],
FILTER ( 'Geography',
Geography[ContinentName] = "Asia" )
)
Boolean
Table

Cumulative Total Measures
 Aggregates values of a column for the currently selected date and all previous dates within
the specified range
 Can be used to derive balances from transactions eg.
 Inventory Stock
 Balances
 Cumulative Balances
 Does not require use of Time Intelligence functions

Cumulative Measure Demo - PowerBI
Cumulative Energy Generated (Checked) =
IF (
MIN ( 'Date'[Date] ) <= MAX ( ‘Output’[Date], ALL ( ‘Output’ ) ) ,
CALCULATE (
SUM ( 'Output'[Energy Generated] ),
FILTER ( ALL ( 'Date'[Date] ), 'Date'[Date] <= MAX ( 'Date'[Date] ) )
)
)

Year-to-Date Total
 TOTALYTD function applies the expression for all data from the start of the year to the
currently selected date in the filter context
Year To Date =
TOTALYTD( <expression>, <dates> [, <filter>] [, <year end date>] )

Year-to-Date Total Demo - PowerBI
Total Energy Generated YTD =
TOTALYTD ( SUM ( 'Output'[Energy Generated] ), 'Date'[Date] )

Year Over Year
 Use time intelligence to calculate an aggregate for the same period last year
 “Last Year” measure is used to compare to “Current Year” measure, and/or to derive a
measure of the change year-over-year

Year-Over-Year Demo – PowerBI
Total Energy Generated Last Year =
CALCULATE ( [Total Energy Generated], SAMEPERIODLASTYEAR ( 'Date'[Date] ) )

Semi-Additive Measures
 Snapshot Fact Table with balance values, such as Inventory or
Account Balances
 These scenarios disallow us from summing across time
 The solution is to sum across all attributes except for time by
filtering for only a single point in time (eg. last date in the period)
 Several functions allow you to adjust filter context to a single
point in time, within the original context period
 FIRSTDATE / LASTDATE
 FIRSTNONBLANK / LASTNONBLANK
 OPENING… / CLOSING…

Semi-Additive Measure Demo -
PowerPivot
Total On Hand Quantity LASTNONBLANK =
CALCULATE (
SUM ( Inventory[OnHandQuantity] ),
LASTNONBLANK ( 'Date'[Date],
CALCULATE ( SUM ( Inventory[OnHandQuantity] ) ) )
)

Disconnected Slicers
Allows you to use a slicer to modify measures
 Measure Switching
 Used to switch between a set of measure values in a container measure

Disconnected Slicers Demo - PowerBI
Setup Steps:
1. Create/identify your target measures (eg. [Energy Exported] & [Energy
Generated])
2. Create disconnected table to use in slicer selection
3. Create background “value selection measure” using MAX()
• Hide this!
4. Create SWITCH measure to use in visualizations

Calculated Column
Patterns
VALUE BINNING

Value Binning
 Used to group similar values, or to bin values for
analysis aka Histograms
 Can bin values based on equality, or inequality
comparisons with the SWITCH() function
 Use Cases:
 Age groups
 Product Groups
 Any kind of frequency distributions

Value Binning Demo - PowerBI
Inventory Age (bin) =
SWITCH (
TRUE (),
'Inventory'[DaysInStock] < 20, "0-20",
"101+"
)

Summary
 DAX is dynamic because you can write measures that correctly evaluate under
their current Evaluation Context
 Filter Context
 Row Context
 Functions are the building blocks of our measures and perform a myriad of
tasks eg. altering Context, aggregating, logical operations, time intelligence,
etc
 Time Intelligence functions require a Date table to operate
 Understanding Tabular Data Modeling will go a long way towards helping your
understanding of DAX

Intro to DAX Patterns

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Editor's Notes