Using Clojure's filter to find entry with minimum value -

i developed function using clojure returns row minimum value determined. here function that:

(#(reduce (fn [r1 r2] (let [v1 (read-string (apply str (clojure.string/split (get r1 %2) (re-pattern " "))))                              v2 (read-string (apply str (clojure.string/split (get r2 %2) (re-pattern " "))))]                      (if (< v1 v2) r1 r2))) %1) [[1 "2007 05 18"] [2 "2004 06 15"] [3 "2004 06 10"]] 1) 

returns:

[3 "2004 06 10"] 

question want implement above function predicate filter function return same result above function. please how do this? thanks

given reasonable assumption have dates, , want row lower date.

this approach using sort-by.

  (sort-by  (fn [[idx date]]               (let [[_ y m d] (re-find #"\d{4} \d{2} \d{2}" date)]                   y))            [[1 "2007 05 18"] [2 "2004 06 15"] [3 "2004 06 10"]]) 

or can parse input string date , avoid regex added benefit of sorting year, month , day.

  (sort-by  (fn [[idx date]]               (.parse (java.text.simpledateformat. "yyyy mm dd") date))             [[1 "2007 05 18"] [2 "2004 06 15"] [3 "2004 06 10"]])      => ([3 "2004 06 10"] [2 "2004 06 15"] [1 "2007 05 18"]) 

then take first or last of result lowest or highest valued row.

using filter makes no sense, since filter doesn't accumulate state, need in order compare rows among each other. (that's you're doing manually reduce function).

filtering sequence predicate give rows matching predicate, nothing relationship between rows themselves.

that's why sort-by idiomatic way sort custom function in situation.

even better, if assume lexicographic sort of stringified date matches order want, can do:

  (sort-by second [[1 "2007 05 18"] [2 "2004 06 15"] [3 "2004 06 10"]])   => ([3 "2004 06 10"] [2 "2004 06 15"] [1 "2007 05 18"])