read lazy seq - how to add the index

Question

I have a toy project where I would like to add some string values into a Redis db. The input is coming from a huge CSV file. The (lazy) function below works fine , but I do not know how to add to the key the indexed value read into the input file - the two commented lines.

Could you give me hint/URL/reference for it? Thank you!


    (defn collector [myfile]
        (with-open [rdr (io/reader myfile)]
          (doseq [line (line-seq rdr)]
               ; [idx (iterate inc 0)]
            (let [[k v1 v2 v3 v4 v5 v6 v7] (clojure.string/split line #",")]
              (red/set db
                (str "key:" k)
               ;(str "key:" k ":" idx)
                (str v1 "-" v5 "-" v6))))))

leetwinski leetwinski · Accepted Answer · 2016-07-05T04:49:48

the best thing you can do without changing your code structure, is to attach the index to the lines seq this way:

(doseq [[idx line] (map-indexed vector (line-seq rdr))] ...)

then the second commented line would work as planned.

(map-indexed vector coll) would pass the two parameters (index and the element of the sequence) to the vector function, making the tuple of them, and destructuring bind [idx line] binds its elements to desired names.

This is a commonly used idiom to index the collection. Also you could do it this way:

(map vector (range) coll), which works the same way as map-indexed, though this idiom is usable to make tuples of any collections:

(map vector (range) [:a :b :c :d] (iterate (partial * 2) 1))

;;=> ([0 :a 1] [1 :b 2] [2 :c 4] [3 :d 8])

read lazy seq - how to add the index

1 Answers