Given
[["foo" "bar" 2] ["biz" "baf" 3]]
how do I get
[{:a "foo" :b "bar" :num 2} {:a "biz" :b "baf" :num 3}]?
In reality my vector has hundreds of vectors that need to have keys added and be converted to hash-maps.
2 Answers
What leetwinski said, or:
(def input [["foo" "bar" 2]["biz" "baf" 3]])
(mapv (fn [[a b num]]
{:a a
:b b
:num num}) input)
If you need to convert a lot of data, maybe mapv is not the best option because it will keep the whole vector in memory at once. Normal map which creates a lazy seq, or a transducer might be better in that case.
3 Comments
THX1137
Great, thanks... the memory aspect is definitely good to keep in mind!
leetwinski
As for me I find this variant to be better than zipmap, because it is more refactoring-friendly and readable
Michiel Borkent
A minor detail: this way is also more performant than zipmap, but we're talking about 22 vs 220 ns so not likely to be noticed.
A general solution:
(defn vectors->maps
"takes a vector of vectors containing values and a vector of keys
and returns a vector of maps such that each value at index n in the value
vector is paired with each key at index n in the keys vector
ex: (vectors->maps [["foo" "bar" 2] ["biz" "baf" 3]], [:a :b :num])
=> [{:a "foo", :b "bar", :num 2} {:a "biz", :b "baf", :num 3}]"
[vectors keys]
(mapv (partial zipmap keys) vectors))
Exercise for the reader: writing a spec for this function and generating tests for it to ferret out any edge cases
(mapv (partial zipmap [:a :b :num]) [["foo" "bar" 2]["biz" "baf" 3]])