Comment by heartofgold

Here is an example to massage/manipulate CSV data.

Stolen from the README page for a clojure CSV parsing library (https://github.com/clojure/data.csv)

    (defn read-column [reader column-index]
      (let [data (read-csv reader)]
        (map #(nth % column-index) data)))
    
    (defn sum-second-column [filename]
      (with-open [reader (io/reader filename)]    ; Read in the CSV file (streaming / lazily)
        (->> (read-column reader 1)               ; Convert to just the first column of data.
             (drop 1)                             ; Drop the first row (the CSV header)
             (map #(Double/parseDouble %))        ; convert each string in this column into double
             (reduce + 0))))                      ; sum the result

Because it's lazy, this code should work regardless of how large the CSV file.