[Java-ML-support] transforming dataset into a different dataset structure

[טל ד. <tal...@gm...>]

Hi, I'd like to transform a raw dataset, loaded from file (e.g. user item
rating),
into a new dataset with a different structure (e.g. user item1rating
item2rating ...)

how can I accomplish this? I tried using indexOf, and use the first field
value as an identifier, on the raw dataset, but it doesn't work.

Any idea how to batch ratings with the same userID in the raw dataset, into
a single instance in the new dataset?

Thanks,
Tal