Clojure: Storing Data for Later UsePosted: July 1, 2011
One of the biggest hurdles I’ve encountered learning Clojure is when to traverse a sequence or merely to apply a function to it, like zipmap. The other hurdle is how to populate local variables properly in a let statement.
The program I am designing to learn Clojure reads a .csv file filled with water meter data. My goal is to extract a premise id and reading, and do something with that data. The premise id is in column 12, zero-indexed at all, and reading is at column 2, zero-indexed by 1.
zipmap takes the values derived from the two map statements, and creates a sequence of values, which is what I wanted. The read-map value can be passed on to other functions.
This solution came from clojure Google group. Enroute to this solution, I tried various ways to populate the map variable, and these did not work or generated a compile-time error. It would be good for someone to write a cookbook that discussed pulling data out of files and storing it in different ways in local variables.
(ns test-csv (:gen-class) (:use clojure.contrib.command-line) (:use clojure-csv.core)) (defn process-file "Process csv file and prints a column in every row" [file-name] (let [data (slurp file-name) rows (parse-csv data) read-map (zipmap (map #(nth % 11 nil) rows) (map #(nth % 1 nil) rows))] (println read-map))) (defn -main [& args] (with-command-line args "Get csv file name" [[file-name ".csv file name" "resultset.csv"]] [[file-name ".csv file name" 1]] (println "file-name:", file-name) (process-file file-name)))