I want to create a vector of maps like this:
[{:patid 0} {:patid 1} {:patid 2}]
=> [{:patid 0} {:patid 1} {:patid 2}]
How would I create a vector of n maps? The closest I've gotten is this:
(defn patientid [n]
(interleave (repeat n :patid) (range n)))
(patientid 3)
=> (:patid 0 :patid 1 :patid 2)
Is there a function to convert this list into maps?
This should do the trick:
(mapv (partial hash-map :patient-id) (range 3))
=> [{:patient-id 0} {:patient-id 1} {:patient-id 2}]
This is mapping (mapv to return a vector as requested) over a range of integers, and creating a map for each one. hash-map is a function that takes key/value pairs, and this uses partial to create a partial function (that's only missing the number). For example, this is slightly longer but functionally equivalent and maybe easier to understand using a map literal:
(mapv (fn [n] {:patient-id n}) (range 3))
I like to keep it simple:
(def map-list
(for [i (range 5)]
{:patient-id i}))
(println map-list)
=> ({:patient-id 0} {:patient-id 1} {:patient-id 2} {:patient-id 3} {:patient-id 4})
If you want it in a vector (my favorite) instead of a lazy list, use vec:
(def map-vec (vec map-list))
(println map-vec)
=> [{:patient-id 0} {:patient-id 1} {:patient-id 2} {:patient-id 3} {:patient-id 4}]
The most efficient way would be this:-
(defn generate-n [n]
(persistent! (loop [out (transient []) x 0]
(if (< x n)
(recur (conj! out {:patient-id x}) (inc x))
out)))
)
Here are some tests results:-
user=> (time (mapv (fn [n] {:patient-id n}) (range 5)))
"Elapsed time: 0.476472 msecs"
[{:patient-id 0} {:patient-id 1} {:patient-id 2} {:patient-id 3} {:patient-id 4}]
user=> (time (mapv (fn [n] {:patient-id n}) (range 5)))
"Elapsed time: 0.1545 msecs"
[{:patient-id 0} {:patient-id 1} {:patient-id 2} {:patient-id 3} {:patient-id 4}]
user=> (time (mapv (fn [n] {:patient-id n}) (range 5)))
"Elapsed time: 0.143853 msecs"
[{:patient-id 0} {:patient-id 1} {:patient-id 2} {:patient-id 3} {:patient-id 4}]
user=> (time (mapv (fn [n] {:patient-id n}) (range 5)))
"Elapsed time: 0.163187 msecs"
[{:patient-id 0} {:patient-id 1} {:patient-id 2} {:patient-id 3} {:patient-id 4}]
With loop recur :-
user=> (time (generate-n 5))
"Elapsed time: 0.033539 msecs"
[{:patient-id 0} {:patient-id 1} {:patient-id 2} {:patient-id 3} {:patient-id 4}]
user=> (time (generate-n 5))
"Elapsed time: 0.032465 msecs"
[{:patient-id 0} {:patient-id 1} {:patient-id 2} {:patient-id 3} {:patient-id 4}]
user=> (time (generate-n 5))
"Elapsed time: 0.031155 msecs"
[{:patient-id 0} {:patient-id 1} {:patient-id 2} {:patient-id 3} {:patient-id 4}]
mapv, which uses reducible/transients internally. You’re measuring the wrong thing.
mapv and my code both are almost same, but in the above Taylor Wood's solution two loops are being used which is not necessary.