29 lines
1 KiB
Clojure
29 lines
1 KiB
Clojure
|
|
; "To categorize a collection by some function, use group-by."
|
|
(= __ (group-by count ["hello" "world" "foo" "bar"]))
|
|
|
|
; "You can simulate filter + remove in one pass"
|
|
(= (get-odds-and-evens [1 2 3 4 5])
|
|
((juxt filter remove) odd? [1 2 3 4 5])
|
|
[[1 3 5] [2 4]])
|
|
|
|
; "You can also group by a primary key"
|
|
(= __
|
|
(group-by :id [{:id 1 :name "Bob"}
|
|
{:id 2 :name "Jennifer"}
|
|
{:id 1 :last-name "Smith"} ]))
|
|
|
|
; "But be careful when you group by a non-required key"
|
|
(= {"Bob" [{:name "Bob" :id 1}]
|
|
"Jennifer" [{:name "Jennifer" :id 2}]
|
|
__ [{:last-name "Smith" :id 1}]}
|
|
(group-by :name [{:id 1 :name "Bob"}
|
|
{:id 2 :name "Jennifer"}
|
|
{:id 1 :last-name "Smith"}]))
|
|
|
|
; "The true power of group-by comes with custom functions"
|
|
(= __
|
|
(group-by #(if (:bad %) :naughty-list :nice-list)
|
|
[{:name "Jimmy" :bad true}
|
|
{:name "Jane" :bad false}
|
|
{:name "Joe" :bad true}]))
|