CODEWITHSUNDEEP
clojure
murtaza52
murtaza52

Reputation: 47441

unable to get sorted-map-by and apply work together

I am having trouble using a custom comparator with sorted-map-by and apply. How do I make the expression below work -

(apply sorted-map-by > {1 "ab" 3 "cs" 2 "vs"})

I get the below exception -

IllegalArgumentException No value supplied for key: [3 "cs"] clojure.lang.PersistentTreeMap.create (PersistentTreeMap.java:87)

Upvotes: 1

Views: 145

Answers (2)

A. Webb
A. Webb

Reputation: 26446

Assuming you are wanting to sort on keys with an existing map, you could use into:

(into (sorted-map-by >) {1 "ab" 3 "cs" 2 "vs"})

This works because (sorted-map-by >) returns an empty sorted map, so using functions like into and assoc will work as expected while the map maintains the sorted order.

;=> {3 "cs", 2 "vs", 1 "ab"}

The sorted-map-by function works on flat arguments:

(sorted-map-by > 1 "ab" 3 "cs" 2 "vs")
;=> {3 "cs", 2 "vs", 1 "ab"}

Applying it to this map would give an odd number of pairs:

(apply list {1 "ab" 3 "cs" 2 "vs"})
;=> ([1 "ab"] [2 "vs"] [3 "cs"])

And it is trying to make every other one a value to a preceding key, hence the error.

Upvotes: 5

Abimaran Kugathasan
Abimaran Kugathasan

Reputation: 32488

You would use apply, if the number of arguments to pass to the function is not known at compile-time. So the best way is to use 

(into (sorted-map-by >) {1 "ab" 3 "cs" 2 "vs"})

Upvotes: 1

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