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5

I have an array of tuples, where each tuple is a 2 tuple with a key and a value. What would be the cleanest way to convert this array of tuples into a hash-map?

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4 Answers 4

up vote 19 down vote accepted 
user=> (into {} [[:a 1] [:b 2]])
{:a 1, :b 2}
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Note that this also works for arrays of two-element arrays -- you'd just have to add a (map vec ...) around the array argument: (into {} (map vec an-array-of-two-element-arrays)). –  Michał Marczyk Dec 1 '10 at 22:16
    
And again, one of those "duh" moments you so often have while using Clojure. Nice answer. –  Isaac Dec 1 '10 at 22:59
    
But a relatively expensive one. –  kotarak Dec 2 '10 at 14:14
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up vote 3 down vote

Assuming that "tupel" means "two-elememt array":

(reduce 
  (fn [m tupel] 
      (assoc m 
            (aget tupel 0) 
            (aget tupel 1))) 
  {} 
  array-of-tupels)
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Nice. If your (to the OP) "array" is in fact a seq, instead of (aget t n) you can use (t n), which is a bit prettier. –  Isaac Dec 1 '10 at 20:49
    
(t n) does not work with sequences. It does with vectors. But then you can simply use (into {} array-of-vectors) instead of the reduce. –  kotarak Dec 2 '10 at 14:12
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up vote 2 down vote 
user=> (def a [[:a 4] [:b 6]])
user=> (apply hash-map (flatten a))
{:a 4, :b 6}
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flatten is overkill for this problem. You can take advantage of the tuples being in the form of a MapEntry (vector of key and value). –  miner49r Apr 22 '11 at 19:12
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up vote 2 down vote

A map is a sequence of MapEntry elements. Each MapEntry is a vector of a key and value. The tuples in the question are already in the form of a MapEntry, which makes things convenient. (That's also why the into solution is a good one.)

user=> (reduce conj {} [[:a 1] [:b 2]])
{:b 2, :a 1}
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