How can I remove an item from a sequence in Clojure?

Question

First, I assume each structure-specific sequences would have different ways to remove an item: Vectors could be by index, List could be remove first or las

Answer 1

There is no single interface for removing things from all of Clojure's data structure types, possibly because of the different performance characteristics.

(disj #{:foo :bar} :foo)       ; => #{:bar}
(dissoc {:foo 1 :bar 2} :foo)  ; => {:bar 2}
(pop [:bar :foo])              ; => [:bar]
(pop (list :foo :bar))         ; => (:bar)

These also work (returning a seq):

(remove #{:foo} #{:foo :bar})      ; => (:bar)
(remove #{:foo} [:foo :bar])       ; => (:bar)
(remove #{:foo} (list :foo :bar))  ; => (:bar)

This doesn't work for hash-maps because when you iterate over a map, you get key/value pairs. But this works:

(remove (fn [[k v]] (#{:foo} k)) {:foo 1 :bar 2})  ; => ([:bar 2])

Answer 2

As an extension of Brian Carper's answer. It depends on what you will be doing with the result. If you are passing the result to something that wants to work on the entire set of data (ie to print it) It is idiomatic to make a seq and use filter or remove to solve the problem lazily. If on the other hand you are modifying the data structure to save for various later uses then creating a seq on it would loose its favorable update characteristics so in this case its better to use the update function specific to that data structure.

Answer 3

Look at the Clojure reference for sequences. filter and remove are what you seek.