Another possible approach. Key idea here is to use partition to create
a sliding window over the lines, plus a sentinel value (I picked "")
before the first line. Pretty sure I like partition over reduce for
this particular example.
(ns examples.convert
(:use [clojure.contrib.duck-streams :only (reader)])
(:use [clojure.contrib.str-utils :only (re-split)]))
(defstruct line :lat :lon :name)
(defn convert [file]
(with-open [r (reader file)]
(doseq [[l1 l2] (partition 2 1 (cons "" (line-seq r)))]
(if (not= l1 l2)
(println (apply struct line (re-split #"," l2)))))))
> I am parsing a file and to compare the current line
> with the previous line of the file. I am using line-seq
> to go thru the file and I thought I would create a
> ref to store the previous line. When I want to update
> the previous line value I can't seem to do it. I've
> never used refs before so I'm sure I'm doing something
> very stupid.
>
> (defstruct line :lat :lon :name)
>
> (defn convert [file]
> (let [prev-line (ref (struct line))]
> (with-open [r (reader file)]
> (doseq [l (line-seq r)]
> (let [ps (split #"," l)
> c-line (struct line (ps 0) (ps 1) (ps 2))]
> (if (not= c-line @pre-line)
> (do ; do stuff here then update pre-line
> (dosync ref-set pre-line (apply struct line (vals c-
> line)))
> (println @pre-line)))))))) ; this prints out all
> nils doesn't seem to work
>
>
>
> Sorry if this email is not formatted correctly. Something is wrong
> with my browser
> currently typing in a textarea. Thanks.
>
>
>
> >
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