33 lines
1.1 KiB
Clojure
33 lines
1.1 KiB
Clojure
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(defn get-odds-and-evens [coll]
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(let [{odds true evens false} (group-by __ coll)]
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[odds evens]))
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(meditations
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"To split a collection categorized by keys use the group-by function."
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(= __ (group-by count ["hello" "world" "foo" "bar"]))
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"Sometimes you want to filter a sequence but also keep the predicate."
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(= (get-odds-and-evens '(1 2 3 4 5))
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[[1 3 5] [2 4]])
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"You can also group by a primary key"
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(= __
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(group-by :id [{:id 1 :name "Bob"}
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{:id 2 :name "Mike"}
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{:id 1 :last-name "Smith"} ]))
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"but be careful when you group by non primary key"
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(= {"Bob" [{:name "Bob" :id 1}], "Mike" [{:name "Mike" :id 2}], __ [{:last-name "Smith" :id 1}]}
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(group-by :name [{:id 1 :name "Bob"}
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{:id 2 :name "Mike"}
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{:id 1 :last-name "Smith"}]))
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"The true power of group-by is using a custom function"
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(= __
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(group-by #(if (:bad %) :nauty-list :nice-list)
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[{:name "Jimmy" :bad true}
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{:name "Jack" :bad false}
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{:name "Joe" :bad true}])))
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