Fix behavior of INNER and LEFT_OUTER joins with empty left table

[vanderzee-anl-gov]

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Description

Current behavior of tablesaw behaves like a right outer join or full outer join should behave if the left table is empty. Based on review of the source code, this appears to be the case because the normal termination for left outer join and inner join is within a loop over the rows of the first table. This commit handles the special case of an empty left table for left outer join and inner join, correctly returning an empty table with the appropriate columns.

Testing

Although it should be fairly simple to test this, I did not take the time to understand your testing framework and add a unit test.

[benmccann]

Although it should be fairly simple to test this, I did not take the time to understand your testing framework and add a unit test.

Like you said, I think it should be pretty easy. You can add a test to DataFrameJoinerTest and then you can run the tests for just that class with cd core and then mvn -Dtest=DataFrameJoinerTest test. Let me know if you have any particular questions

[vanderzee-anl-gov]

I haven't used maven much before, but I have now added tests that illustrate the difference in behavior with and without my suggested block of code. They fail without my code and pass when it is included.

[benmccann]

thanks for adding a test!

[benmccann]

You could condense the first four lines into two:

    Table leftTable = Table.create(StringColumn.create("Animal"));
    Table joined = leftTable.joinOn("Animal").inner(ANIMAL_NAMES);