String Replacing in Regex

Question

I am trying to replace text in string using regex. I accomplished it in c# using the same pattern but in swift its not working as per needed.

Here is my code:

var pattern = "\\d(\\()*[x]"

let oldString = "2x + 3 + x2 +2(x)"

let newString = oldString.stringByReplacingOccurrencesOfString(pattern, withString:"*" as String, options:NSStringCompareOptions.RegularExpressionSearch, range:nil)


print(newString)

What I want after replacement is :

"2*x + 3 +x2 + 2*(x)"

What I am getting is :

"* + 3 + x2 +*)"

ramana_k · Accepted Answer · 2015-10-06 01:19:16Z

1

Try this:

(?<=\d)(?=x)|(?<=\d)(?=\()

This pattern matches not any characters in the given string, but zero width positions in between characters.

For example, (?<=\d)(?=x) This matches a position in between a digit and 'x'

(?<= is look behind assertion (?= is look ahead.

(?<=\d)(?=\()    This matches the position between a digit and '('

So the pattern before escaping:

(?<=\d)(?=x)|(?<=\d)(?=\()

Pattern, after escaping the parentheses and '\'

\(?<=\\d\)\(?=x\)|\(?<=\\d\)\(?=\\\(\)

answered Oct 6, 2015 at 1:19

ramana_k

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