clojure: add index to vector of maps

Question

I have a vector of maps. I want to associate an index element for each element.

Example:

(append-index [{:name "foo"} {:name "bar"} {:name "baz"}])

should return

[{:name "foo" :index 1} {:name "bar" :index 2} {:name "baz" :index 3}]

What is the best way to implement append-index function?

I just want the position in the vector as index. I think I actually found a function that will do what I want so I'll just answer this myself and close this. — mikkom
– mikkom, Commented Dec 28, 2015 at 9:44
Side note: if you think about it, it doesn't make much sense to add the index on the map. You can add it when you fetch it. Be lazy my friend. — m0skit0
– m0skit0, Commented Dec 28, 2015 at 9:45
This is part of a larger thing that involves fetching recursive structure from database via external library and then sorting it (at html/javascript side). — mikkom
– mikkom, Commented Dec 28, 2015 at 9:49

Leonid Beschastny · Accepted Answer · 2015-12-28 09:48:35Z

7

First of all, Clojure starts counting vector elements from 0, so you probably want to get

[{:index 0, :name "foo"} {:index 1, :name "bar"} {:index 2, :name "baz"}]

You could do it pretty easily with map-indexed function

(defn append-index [coll]
  (map-indexed #(assoc %2 :index %1) coll))

answered Dec 28, 2015 at 9:48

Leonid Beschastny

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Comments

leetwinski · Accepted Answer · 2015-12-28 15:47:24Z

1

just adding some fun:

(defn append-index [items]
  (map assoc items (repeat :index) (range)))

answered Dec 28, 2015 at 15:47

leetwinski

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