e r l a n g : c o o k b o o k

This Web

WebHome 
WebChanges 
TOC
NewRecipe 
WebTopicList 
WebStatistics 

All Webs

Chicken
Cookbook
Erlang
Know
Main
Plugins
Sandbox
Scm
TWiki  

Erlang Links

Erlang.org
Erlang Wiki
ErlMan
Erlang Wiki
The Jungerl
Erlang-fr.org
Joe Armstrong
Lambda the Ultimate

Erlang Web Ring

[Prev]: Joe Armstrong's Page
[Next]: Joe Armstrong's Page

Reversing a String by Words or Characters

Problem

You want to reverse the words or characters in a string

Solution

In this case, you have to choose between the lists and string modules. If you intend to work only with characters, it's most efficient to use the lists module. For words, the string module is what you want, since it has ready-made functions for chunking up strings by words.

lists:reverse will reverse the characters of a string:

1> lists:reverse("Hello, World!"). "!dlroW ,olleH"

Reversing a string by words is a combination of list and string operations:

1> lists:flatmap(fun(A) -> A ++ " " end, "", 1> (lists:reverse( string:tokens("Hello, World!", " ")))). "World! Hello, "

Discussion

Obviously my simple two-line function appends an extra space on the end. You could get rid of this by doing something more complicated, such as:

1> A = lists:flatmap(fun(A) -> A ++ " " end, "", 1> (lists:reverse( string:tokens("Hello, World!", " ")))). "World! Hello, " 2> string:substr(A, 1, length(A) - 1). "World! Hello,"

-- BrentAFulgham - 20 Aug 2004

CookbookForm
TopicType:	Recipe
ParentTopic:	StringRecipes
TopicOrder:	070