Question

I would like to implement a fast “group by” like feature in Java.
I have a List<List<String>> and I want to iterate through based on groupping on different indexes.

For example:

A1 B1 C1 value_1 A1 B1 C2 value_2 A1 B2 C1 value_3  A1 B2 C2 value_4

I want some aggregations using groupping on first and third column.
And I want it to be fast – avoid calculating every sum at every query.
The values from the “table” are changing constantly.
Any thoughts?

Answer 1

Java is not well suited for that task. I’d rather go with an in memory SQL database. First dump the values to a table and then retrieve the rows with a select SQL statement grouping, ordering or summing by different columns.