Calculation Groups - color 1 slide per page.pdf

Introducing calculation groups
o New feature DAX since late 2019
o Reduce the number of measures, by automating
repetitive patterns
o Useful in multiple scenarios
o Require some deep understanding of DAX

Basic measures
Any model contains several basic measures, like the following four:
Sales Amount := SUMX ( Sales, Sales[Quantity] * Sales[Net Price] )
Total Cost := SUMX ( Sales, Sales[Quantity] * Sales[Unit Cost] )
Margin := [Sales Amount] - [Total Cost]
Sales Quantity := SUM ( Sales[Quantity] )

Aggregation measures
Most measures are useful also in a pre-aggregated way.
For example, YTD, MTD, SPLY are common aggregations required for most measures
YTD Sales Amount :=
CALCULATE (
[Sales Amount],
DATESYTD ( 'Date'[Date] )
)
YTD Total Cost :=
CALCULATE (
[Total Cost],
)
YTD Margin :=
CALCULATE (
[Margin],
)
YTD Sales Quantity :=
CALCULATE (
[Sales Quantity],
)

Basic measures and their variations
o One measure for each variation/basic measure
o 10 basic measures, 6 variations means 60 new
measures
o Every new basic measure requires all the variations
o The model quickly becomes messy
• Finding consistent names is hard
• Finding the right measure is troublesome
• Any update requires significant effort

The SWITCH solution
Before calculation groups, SWITCH has been widely used to reduce the number of
measures
VAR Selection = SELECTEDVALUE ( 'Time Intelligence'[Aggregation] )
RETURN
SWITCH (
Selection,
"CY", [Sales Amount],
"YTD", [YTD Sales Amount],
"PY", [PY Sales Amount],
"QTD", [QTD Sales Amount]
)

Calculation items are “patterns”
You define a pattern, which is implemented for each measure automatically
YTD <Measure> :=
CALCULATE (
<Measure>,
)

Calculation groups
Calculation groups combine several calculation items in a single group.
Consider a possible syntax like the following one (note: this syntax does not exists)
CALCULATION GROUP "Time Intelligence"
ITEM CY := <Measure>
ITEM PY := CALCULATE ( <Measure>, SAMPEPERIODLASTYEAR ( 'Date'[Date] ) )
ITEM QTD := CALCULATE ( <Measure>, DATESQTD ( 'Date'[Date] ) )
ITEM YTD := CALCULATE ( <Measure>, DATESYTD ( 'Date'[Date] ) )

Creating calculation groups
o Currently, only Tabular Editor lets you define calc
groups
o Download from https://tabulareditor.github.io/
o Free, open source project written by Daniel Otykier
o Offers lots of features, including calc groups

SELECTEDMEASURE
o SELECTEDMEASURE is a special function
o Acts as a placeholder for the measure changed
o Available only in calculation items

Changing the format string
Calculation items lets you change the format string too, if the default one does not fit well.
Can be dynamically changed, using SELECTEDMEASUREFORMATSTRING
CALCULATION GROUP "Time Intelligence"
ITEM CY := SELECTEDMEASURE ()
ITEM Growth :=
DIVIDE (
SELECTEDMEASURE (),
CALCULATE (
SELECTEDMEASURE (),
SAMPEPERIODLASTYEAR ( 'Date'[Date] )
)
)
Format as a decimal number
Format as a percentage

Excluding specific measures
Some calculation items might not be applicable to specific measures.
ISSELECTEDMEASURE lets you make distinctions
IF (
ISSELECTEDMEASURE (
[Sales Amount], [Gross Amount],
[Discount Amount], [Sales Quantity],
[Total Cost], [Margin]
),
DIVIDE (
SELECTEDMEASURE (),
COUNTROWS ( 'Date' )
)
)

SELECTEDMEASURENAME
SELECTEDMEASURENAME returns the name of the selected measure, as a string.
IF (
NOT ( SELECTEDMEASURENAME () = "Margin %" ),
DIVIDE (
SELECTEDMEASURE (),
)
)

Using calculation items in DAX
Calculation items can be used in a DAX expression by using CALCULATE
CALCULATE (
[Sales Amount],
'Time Intelligence'[Time calc] = "YTD"
)
-- the previous code becomes
CALCULATE (
CALCULATE (
[Sales Amount],
)
)
--
-- Calculation Item: YTD
--
CALCULATE (
SELECTEDMEASURE (),
)

Calculation item application
A calculation item is first applied, then evaluated.
The two steps happen in different moments, it is important to understand it well
CALCULATE (
[Sales Amount],
)
CALCULATE (
CALCULATE (
[Sales Amount],
)
)
--
--
CALCULATE (
SELECTEDMEASURE (),
)

Application happens on measure references
A measure reference is needed to perform calculation item application
CALCULATE (
SUMX (
Sales,
Sales[Quantity] * Sales[Net Price]
),
)
CALCULATE (
SUMX (
Sales,
Sales[Quantity] * Sales[Net Price]
)
)
--
--
CALCULATE (
SELECTEDMEASURE (),
)

Application happens on every measure
All the measures in the expression are subject to calculation item application
CALCULATE (
DIVIDE (
[Total Cost],
[Sales Amount]
),
)
CALCULATE (
DIVIDE (
CALCULATE (
[Total Cost],
),
CALCULATE (
[Sales Amount],
)
)
)
--
--
CALCULATE (
SELECTEDMEASURE (),
)

Application happens before evaluation
All the measures in the expression are subject to calculation item application
CALCULATE (
CALCULATE (
[Sales Amount],
'Date'[Calendar Year] = "CY 2009"
),
'Time Intelligence'[Time calc] = "YTD",
)
CALCULATE (
CALCULATE (
CALCULATE (
[Sales Amount],
),
),
)
--
--
CALCULATE (
SELECTEDMEASURE (),
)
1
2
3
The result is YTD of
2009, not 2008

Calculation items on complex expressions
Using calculation items on complex expressions (anything more complex than a single
measure reference) results in unexpected behaviors.
CALCULATE (
DIVIDE (
[Sales Amount],
SUMX (
VALUES ( 'Date'[Calendar Year month] ),
IF (
[Sales Amount] > 0,
[# Working Days]
)
)
),
)

Application leads to a wrong evaluation
CALCULATE (
DIVIDE (
CALCULATE (
[Sales Amount],
),
SUMX (
IF (
CALCULATE (
[Sales Amount],
) > 0,
CALCULATE (
[# Working Days],
)
)
)
),
)
CALCULATE (
DIVIDE (
[Sales Amount],
SUMX (
IF (
[Sales Amount] > 0,
[# Working Days]
)
)
),
)

Always use a single measure expression
Using a single measure as the expression to modify with a calculation item, leads to a much
better (and predictable) result
Sales WD :=
DIVIDE (
[Sales Amount],
SUMX (
IF (
[Sales Amount] > 0,
[# Working Days]
)
)
)
CALCULATE (
[Sales WD],
)

Implicit measures
o Calculation groups work with measures only
o Therefore, if a calculation group is created, implicit
measures are disabled
o Best practice: expose measures only
Measures can be used in reports
Columns cannot be aggregated

Multiple calculation groups in a report

Multiple calculation groups
A single model may contain multiple calculation groups
-------------------------------------
-- 'Time Intelligence'[Time calc]
-------------------------------------
--
--
CALCULATE (
SELECTEDMEASURE (),
)
-------------------------------------
-- 'Averages'[Averages]
-------------------------------------
--
-- Calculation Item: Daily AVG
--
DIVIDE (
SELECTEDMEASURE (),
)

Multiple calculation groups in DAX
In a single CALCULATE statement, one can apply multiple calculation groups.
The developer needs to define the order of application of the calculation groups.
CALCULATE (
[Sales Amount],
'Averages'[Averages] = "Daily AVG"
)

Daily AVG applied first
CALCULATE (
[Sales Amount],
)
CALCULATE (
DIVIDE (
[Sales Amount],
),
)
DIVIDE (
CALCULATE (
[Sales Amount],
),
)

YTD applied first
CALCULATE (
[Sales Amount],
)
CALCULATE (
CALCULATE (
[Sales Amount],
),
)
CALCULATE (
DIVIDE (
[Sales Amount],
),
)

Multiple calculation groups
The precedence defines which of the formulas is generated by the application of a
calculation group. The higher the precedence, the earlier the application.
--
-- Daily Average applied first
--
DIVIDE (
CALCULATE (
[Sales Amount],
),
)
--
-- YTD applied first
--
CALCULATE (
DIVIDE (
[Sales Amount],
),
)

Calculation group precedence
o When using multiple calculation groups
o The application follows the precedence
o Higher precedence means earlier application
o Remember: application, not evaluation
o Evaluation happens after the application, on the
resulting formula

Reusing calculation items
In a calculation item you can use CALCULATE to invoke another calculation item, even if it
belongs to the same group
-------------------------------------------------------
-- Calculation Item: 'Time Intelligence'[YOY%]
-------------------------------------------------------
DIVIDE (
CALCULATE (
SELECTEDMEASURE (),
'Time Intelligence'[Time calc] = "YOY"
),
CALCULATE (
SELECTEDMEASURE (),
'Time Intelligence'[Time calc] = "PY"
)
)

Recursion in calculation items
By calling a calculation item from inside another calculation item, you might obtain a recursive
definition. In other words, an infinite loop. DAX does not support recursive definitions.
--
-- Calculation Item: Loop A
--
CALCULATE (
SELECTEDMEASURE (),
Infinite[Loop] = "Loop B"
)
--
-- Calculation Item: Loop B
--
CALCULATE (
SELECTEDMEASURE (),
Infinite[Loop] = "Loop A"
)
CALCULATE (
[Sales Amount],
Infinite[Loop] = "Loop A"
)

Recursion through measures
Recursion might appear in less-evident scenarios, like the following where the infinite loop
appears through a couple of measures.
--
-- Measures definition
--
MA := CALCULATE ( [Sales Amount], Infinite[Loop] = "A" )
MB := CALCULATE ( [Sales Amount], Infinite[Loop] = "B" )
-------------------------------------------------------
-- Calculation Group: Infinite[Loop]
-------------------------------------------------------
--
-- Calculation Item: A
--
[MB]
--
-- Calculation Item: B
--
[MA]
CALCULATE (
[Sales Amount],
Infinite[Loop] = "A"
)

Rule #1: Do not use complex expressions
CALCULATE (
DIVIDE (
[Sales Amount],
SUMX (
IF (
[Sales Amount] > 0,
[# Working Days]
)
)
),
)

Rule #2: Avoid recursion
-------------------------------------------------------
-- Calculation Item: 'Time Intelligence'[YOY%]
-------------------------------------------------------
DIVIDE (
CALCULATE (
SELECTEDMEASURE (),
'Time Intelligence'[Time calc] = "YOY"
),
CALCULATE (
SELECTEDMEASURE (),
'Time Intelligence'[Time calc] = "PY"
)
)

Calculation group best practices
o Only two rules:
• Do not use complex expressions when applying a
calculation item – only use a single measure.
• Do not use any kind of recursion, including the
simplest sideways recursion.

Calculation Groups - color 1 slide per page.pdf

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