can someone elaborate when to use sum , lookup and select in easy to understand way. i have read it from anapedia but still struggling
Another great way to think about which function to use is based on what is being used as the mapping module or what you are using to bridge the gap in dimensions.
1. Dimensionality of the mapping match with the target module - LOOKUP ( the format of the line item in the mapping module must match a dimension in the source )
2. Dimensionality of the mapping match the source module - SUM ( the format of the line item in the mapping module must match the dimensionality of the target )
Finally, use SELECT when you only want to retrieve data from a specific list item. Use sparingly and only when referencing top level list items.
SUM: You use this function when you want to aggregate the numbers based on the list formatted line item in the source module. This is considered to be Many to One relationship - meaning numbers from multiple items will be consolidated and the result will be shown in one single item.
LOOKUP: (Used in the scenario when there is a mismatch in dimensionality) You use this function when you want to get attribute(s) or numbers related to the list which is not the dimension in your target module. Similar to what excel does but in Anaplan we have concept of dimensionality. It is also used in the Top down approach (i.e., Cascading the values from Parent to Child)
SELECT: (Used in the scenario when there is a mismatch in dimensionality) You use this function when you want to get the data of any particular list member of the source module which is not the dimension in target module. This function is no longer being used on Lists anymore due to Scalability issues. It is restricted to Versions and some Time Periods Like (YTD,YTG and All Periods)
Here's a useful diagram showing the basic usage:
from The Bedford Coach - Key Formulas - SUM vs LOOKUP vs SELECT (bedfordconsulting.co.uk)