Why does filter not return the result of predicate function?

Question

I am starting to learn Clojure, but I don't understand why the below code doesn't works as expected.

Given a string, I want it to print all words longer than 2 characters with the first letter capitalized.

Expected output: ("Fine" "Day")
Actual output: ("fine" "day")

(ns exploring
    (:require [clojure.contrib.string :as str]))

(defn a-function [word]
    "Capitaliza todas palavras maiores que 2 chars"
    (if (>(count word ) 2) (str/capitalize word)))

(use '[clojure.contrib.str-utils :only (re-split)])
(filter a-function (re-split #"\W+" "A fine day it is"))

Answer 1

I would use map in addition to filter:

(ns exploring
  (:require [clojure.string :as str])
  (:use '[clojure.contrib.str-utils :only (re-split)])

(def a-function
  [word]
  (> (count word) 2))

(map str/capitalize
     (filter a-function
             (re-split #"\W+" "A fine day it is")))

Answer 2

您可以将keep与原始a-function ：

(keep a-function (re-split #"\W+" "A fine day it is"))

Answer 3

If the order in which the capitalized words are returned is not important you can also do:

(reduce #(if (> (count %2) 2) (cons (str/capitalize %2) %) %) nil (re-split #"\W+" "A fine day it is"))

Resulting in ("Day" "Fine")

I'm not claiming this is better, just another way to solve the same problem.