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January 3, 2020

Clojure Goodness: Trimming Strings

In the clojure.string namespace we can find several useful function for working with strings. If we want to trim a string we can choose for the trim, trial, trimr and trim-newline functions. To trim all characters before a string we must use the triml function. To remove all space characters after a string we use trimr. To remove space characters both before and after a string we can use the trim function. Finally if we only want to remove the newline and/or return characters we use the trim-newline function.

In the following example we use the different trim functions on strings:

(ns mrhaki.sample
  (:require [clojure.test :refer [is]]
            [clojure.string :refer [trim triml trimr trim-newline]]))

;; The trim function removes spaces before and after the string.
(is (= "mrhaki" (trim " mrhaki ")))
;; Tabs are also trimmed.
(is (= "mrhaki" (trim "\t mrhaki ")))
;; Return and/or newline characters are also trimmed.
(is (= "mrhaki" (trim "\tmrhaki \r\n")))
;; Character literals that should be trimmed are trimmed.
(is (= "mrhaki" (trim (str \tab \space " mrhaki " \newline))))

;; The triml function removes spaces before the string (trim left).
(is (= "mrhaki " (triml " mrhaki ")))
(is (= "mrhaki " (triml "\t mrhaki ")))
(is (= "mrhaki " (triml "\nmrhaki ")))
(is (= "mrhaki " (triml (str \return \newline " mrhaki "))))

;; The trimr function removes spaces after the string (trim right).
(is (= " mrhaki" (trimr " mrhaki ")))
(is (= " mrhaki" (trimr " mrhaki\t")))
(is (= " mrhaki" (trimr (str " mrhaki " \newline))))

;; The trim-newline function removes only newline from string.
(is (= "mrhaki " (trim-newline (str "mrhaki " \newline))))
(is (= "mrhaki " (trim-newline (str "mrhaki " \return \newline))))
(is (= "mrhaki " (trim-newline "mrhaki \r\n")))
(is (= "mrhaki " (trim-newline "mrhaki ")))

Written with Clojure 1.10.1.