c# - is there a elegant way to parse a word and add spaces before capital letters

Question

i need to parse some data and i want to convert

AutomaticTrackingSystem

to

Automatic Tracking System

essentially putting a space before any capital letter (besides the first one of course)

Answer 1

You can use lookarounds, e.g:

string[] tests = {
   "AutomaticTrackingSystem",
   "XMLEditor",
};

Regex r = new Regex(@"(?!^)(?=[A-Z])");
foreach (string test in tests) {
   Console.WriteLine(r.Replace(test, " "));
}

This prints (as seen on ideone.com):

Automatic Tracking System
X M L Editor

The regex (?!^)(?=[A-Z]) consists of two assertions:

• (?!^) - i.e. we're not at the beginning of the string
• (?=[A-Z]) - i.e. we're just before an uppercase letter

Related questions

• How do I convert CamelCase into human-readable names in Java?
• How does the regular expression (?<=#)[^#]+(?=#) work?

References

• regular-expressions.info/Lookarounds

---

Splitting the difference

Here's where using assertions really make a difference, when you have several different rules, and/or you want to Split instead of Replace. This example combines both:

string[] tests = {
   "AutomaticTrackingSystem",
   "XMLEditor",
   "AnXMLAndXSLT2.0Tool",
};

Regex r = new Regex(
   @"  (?<=[A-Z])(?=[A-Z][a-z])    # UC before me, UC lc after me
    |  (?<=[^A-Z])(?=[A-Z])        # Not UC before me, UC after me
    |  (?<=[A-Za-z])(?=[^A-Za-z])  # Letter before me, non letter after me
    ",
   RegexOptions.IgnorePatternWhitespace
);
foreach (string test in tests) {
   foreach (string part in r.Split(test)) {
      Console.Write("[" + part + "]");
   }
   Console.WriteLine();
}

This prints (as seen on ideone.com):

[Automatic][Tracking][System]
[XML][Editor]
[An][XML][And][XSLT][2.0][Tool]

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