Subset And Apply Problems

Tom Martens explains a class of generic data processing problems:

Subset and Apply means that I have a dataset of some rows where due to some conditions all the rows have to be put into a bucket and then a function has to be applied to each bucket.

The simple problem can be solved by a GROUP BY using T-SQL, the not so simple problem requires that all columns and rows of the dataset have to be retained for further processing, even if these columns are not used to subset or bucket the rows in your dataset.

One quick example of this is running totals of orders for each customer, which Tom answers using T-SQL, R, and Power BI.  Click through for those three solutions.

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