CODEWITHSUNDEEP
clojure
Mars
Mars

Reputation: 8854

How to convert map to a sequence?

Answers to this question explain how to convert maps, sequences, etc. to various sequences and collections, but do not say how to convert a map to a sequence of alternating keys and values. Here is one way:

(apply concat {:a 1 :b 2})
=> (:b 2 :a 1)

Some alternatives that one might naively think would produce the same result, don't, including passing the map to vec, vector, seq, sequence, into [], into (), and flatten. (Sometimes it's easier to try it than to think it through.)

Is there anything simpler than apply concat?

Upvotes: 2

Views: 2031

Answers (2)

KobbyPemson
KobbyPemson

Reputation: 2539

You can also do 

(mapcat identity {:a 1 :b 2})

or 

(mapcat seq {:a 1 :b 2})

Upvotes: 3

Thumbnail
Thumbnail

Reputation: 13473

As @noisesmith gently hints below, the following answer is seductive but wrong: left as a warning to other unwary souls! Counterexample: 

((comp flatten seq) {[1 2] [3 4], 5 [6 7]})
; (1 2 3 4 5 6 7)

(comp flatten seq) does the job: 

((comp flatten seq) {1 2, 3 4})
; (1 2 3 4)

But flatten on its own doesn't: 

(flatten {1 2, 3 4})
; ()

I'm surprised it doesn't work, and in that case it should return nil, not ().

None of the others you mention: vec, vector ... , does anything to the individual [key value] pairs that the map presents itself as a sequence of.

Upvotes: 1

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