Question

I’m not sure if “token replace” is the right phrase but here is what i’m trying to do:

In a string if I find two or more consecutive white spaces (\s) aka – spaces, new lines, tabs etc. I want to replace whatever it matched with only one instance of itself.

Example:

a   b   b 

would become

a b b

and:

a


b


c

Would become:

a

b

c

Can this be done using .net regex?

Answer 1

You’ll need to use this if you want to correctly replace double new-lines as well as spaces:

string input = @"a


b


c  d  e";

string result = Regex.Replace(input, @"(\r\n|\s)\1", "$1");

The \1 will look for the character(s) matched by the group (\s|\r\n), and the $1 in the replacement string will replace the match with just a single instance of the group.

If you want to replace more than one duplicate (i.e. 3 in a row) with a single instance, you’ll need to use @"(\r\n|\s)\1+" as the pattern, but a side effect of this will be:

a


b


c

will be reduced to:

a
b
c