Doing one-to-one merges
The remainder of this chapter will explore combining data horizontally; that is, merging columns from a data table with columns from another data table. Borrowing from SQL development, we typically talk about such operations as join operations: left joins, right joins, inner joins, and outer joins. This recipe examines one-to-one merges, where the merge-by values are unduplicated in both files. Subsequent recipes will demonstrate one-to-many merges, where the merge-by values are duplicated on the right data table, and many-to-many merges, where merge-by values are duplicated on both the left and right data tables.
We often speak of the left and right sides of a merge, a convention that we will follow throughout this chapter. But this is of no real consequence, other than for clarity of exposition. We can accomplish exactly the same thing with a merge if A were the left data table and B were the right data table, as we could if the reverse were true.
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