Chapter 02 - Strings

String (str) Function

(str 'hello) 
  => "hello"

• You can also use the str function to combine terms

(str 'hello " world") 
  => "hello world"

Get Function

Returns the value mapped to key, not-found or nil if key not present. If used on a string, you can pass an index position an retrieve a character

Note: The \C indicates that this is a character

(get "Characters" 0 )
  => \C

Count Function

Count the characters in a string

(count "Hello World")
  => 11

Subs

Returns the substring of s beginning at start inclusive, and ending at end (defaults to length of string), exclusive.

(sub "Hello World" 6 11)
  => "World"

Working with the Clojure String Library

clojure.string/join

Note: In order to use clojure.string, you must import it into your name space. This can be done using the require function. Additionally, you can call it and rename it to make using it a bit easier. You would use (require '[clojure.string :as string]) to call it in and use it as the symbol string

You can use string/join to combine strings together...

(string/join '(1 2 3))
  => "123"

Or you can even insert characters between each element

(string/join ", " '(1 2 3))
  => "1, 2, 3"

clojure.string/split-lines

Splits s on \n or \r\n

(string/split-lines "1\n2\n3")
  => "1" "2" "3"

clojure.string/reverse

Reverse a string

(string/reverse "hello")
  => "elloh"

clojure.string/index-of

Return index of value (string or char) in s, optionally searching forward from from-index or nil if not found. In other words, you can add an integer telling the indexer which element to start at as in the 3rd example below.

(index-of "ababc" "a")
;;=> 0

(index-of "ababc" "ab")
;;=> 0

(index-of "ababc" "ab" 1)
;;=> 2

clojure.string/last-index-of

Return last index of value (string or char) in s, optionally searching backward from from-index or nil if not found. In layman's terms, The integer indicates to start at position x and look back from that point for the term.

(last-index-of "abcde" "c")
;;=>2

(last-index-of "abcde" "e" 3)
;;=> nil

(last-index-of "abcde" "e" 4)
;;=> 4

clojure.string/trim

Removes whitespace from both ends of string. Note: Escape sequences count as white space and will be removed"

(string/trim " \nhello world \t \n")
;;=> "hello world"

Querying Strings

Is it a character?

(char? \c)
;;=> true

(char? "c")
;;=> false

Is it a string?

(string? \b)
;;=> false

(string "b")
;;=> true

Is it blank?

Note: This function is a part of the clojure.string library. In addition, escaped characters don't count as characters.

(string/blank? "")
;;=> true

(string/blank? " \n \t")
;;=> true

(string/blank? "Pizza \t and \t Turkey")
;;=> false