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Clojure Data Analysis Cookbook - Second Edition by Eric Rochester

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Defining new Cascalog operators

Cascalog comes with a number of operators; however, you'll often need to define your own, as we saw in the Aggregating data in Cascalog recipe.

For different uses, Cascalog defines a number of different categories of operators, each with different properties. Some are run in the map phase of processing, and some are run in the reduce phase. The ones in the map phase can use a number of extra optimizations, so if you can push some of your processing into that stage, you'll get better performance. In this recipe, you'll see which categories of operators are on the map side and which are on the reduce side. We'll also provide an example of each and see how they fit into the larger processing model.

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