By default, an input iterator on an IMDC produces all columns stored in the IMDC. The call that returns a default input iterator is InMemoryDataCollection::newRowIterator().
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To return an input iterator that produces a subset of columns stored in the IMDC, use this call:
InMemoryDataCollection::newRowIterator( ImmutableList<Integer> projectionColumnIndexes)
Each integer in list is the index of a column to include in the subset.