Creating QUARTILE function within Anaplan
This is a method of building the Excel “Quartile” function within Anaplan – it requires 11 Line items, requires that the Data dimension has a ‘top level’ value, and uses the RANK function which has an upper limit of 50 million cells. To start, create a module (or use an existing calc module) dimensioned by your base data and whatever dimensions are necessary. In my example, I used just a single "Data List" dimension.
In that module, add the following formulas:
Data Module
Count = 1
Rank = RANK({Value} <wherever that is in the model>, ASCENDING, SEQUENTIAL)
The count summary method must be set to Sum, the Rank summary method can be set to None.
Then create a summary module, without the base data dimension but all other dimensions (if any) the same.
If you are replicating the QUARTILE.INC then add the following formulas:
Summary Module
Number of Items = Data Module.Count
Q1 item marker = 0.25 * (Number of Items  1) + 1
Q2 item marker = 0.5 * (Number of Items  1) + 1
Q3 item marker = 0.75 * (Number of Items  1) + 1
If you are replicating the QUARTILE.EXC then the section after the percentage value should be changed to * (Number of Items + 1) for all three item marker formulas – For example:
Q1 item marker = 0.25 * (Number of Items + 1)
This now tells us which ranked item should selected for the Median (Q2), First Quartile (Q1), and Top Quartile (Q3) values.
Then go back to the Data Modules and we will build three line items that pull out the correct items, or interpolate between them if necessary:
Data Module
1st Quartile = IF ABS(Rank  Summary Module.'Q1 item marker') < 1 THEN {Value} * (1  ABS(Rank  Summary Module.'Q1 item marker')) ELSE 0
2nd Quartile = IF ABS(Rank  Summary Module.'Q2 item marker') < 1 THEN {Value} * (1  ABS(Rank  Summary Module.'Q2 item marker')) ELSE 0
3rd Quartile = IF ABS(Rank  Summary Module.'Q3 item marker') < 1 THEN {Value} * (1  ABS(Rank  Summary Module.'Q3 item marker')) ELSE 0
These must all have the summary method of Sum. The IF clause in this formula will only pull through values whose rank matches the appropriate median/quartile value, and the THEN clause will take that only the specific value if it lands exactly, or interpolate in situations where the median lies between two values, and the two partial values will be automatically added up by the summary method of “Sum”.
Then finally, in the Summary Module, we add 3 more line items to pull the correct summarized value. Since the Data dimension is not present in the Summary Module, the default behavior is to take the top level summarized value:
Summary Module
1st quartile = Data Module.'1st Quartile'
2nd quartile = Data Module.'2nd Quartile'
3rd quartile = Data Module.'3rd Quartile'
From there, those summarized line items can be used however is needed downstream.
One thing to note, if only the Top Quartile value is needed, then the Q1 and Q2 line items in both the Data and Summary module can be removed.
Screenshots of my Data and Summary modules with a very simple data set, recreating the QUARTILE.INC function, and comparing it to the Excel result:
Answers

Great stuff and thanks for sharing.
Have you reached any performance issue related to the use of the RANK() function?
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Thanks for the feedback! I have only tested this solution on moderately sized data sets, not any nearing the 50 million limit, so I have not been greatly impacted by the calculation time. This article discuss the reasoning for the limit: https://help.anaplan.com/anapedia/Content/Calculation_Functions/All/RANK.html
The ranking of the values is a critical step in the process, I don't think there is an easy way to do it without the RANK formula. If a data set larger than 50,000,000 were to require the Quartile function a workaround would be necessary  possibly a Sort and then import into a dummy list? But I believe that would be very time intensive and really only work if no other dimensions were applied to the base data.
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