Remove whitespace and multiple line from string?

Question

I have a string , like this:

"  \n assddd\n\n\n\n\n adjf fff dd \n\n\n\n       tjhfhdf \n      "

I want the result is:

"assddd\nadjffffdd\ntjhfhdf". 

1: I used trimmingCharacters to remove the beginning and the ending:

let title = "  \n assddd\n\n\n\n\n adjf fff dd \n\n\n\n       tjhfhdf \n".trimmingCharacters(in: .whitespacesAndNewlines)

2: remove whitespaces

let result = title.replacingOccurrences(of: " ", with: "")

but, how to keep the first "\n" between the character and remove other "\n" ？

Answer 1

You can find two or more consecutive newline characters with a regular expression, and replace them with a single newline character. Example:

let s1 = "AA\n\nBB\nCC\n\n\n\n\nDD"
let s2 = s1.replacingOccurrences(of: "\\n{2,}", with: "\n", options: .regularExpression)

print(s1.debugDescription) // "AA\n\nBB\nCC\n\n\n\n\nDD"
print(s2.debugDescription) // "AA\nBB\nCC\nDD"

Applied to your case:

let title = "  \n assddd\n\n\n\n\n adjf fff dd \n\n\n\n       tjhfhdf \n      "

let result = title.trimmingCharacters(in: .whitespacesAndNewlines)
    .replacingOccurrences(of: " ", with: "")
    .replacingOccurrences(of: "\\n{2,}", with: "\n", options: .regularExpression)

print(result.debugDescription) // "assddd\nadjffffdd\ntjhfhdf"

Answer 2

Starting with your sample text, we can trim the ends:

let sample = "  \n assddd\n\n\n\n\n adjf fff dd \n\n\n\n       tjhfhdf \n      "
let trimmedEnds = sample.trimmingCharacters(in: .whitespacesAndNewlines)

If you just want to remove space and compress newlines:

let noHorizSpace = trimmedEnds.replacingOccurrences(of: " ", with: "") // remove all spaces
let singleVertSpace = noHorizSpace.replacingOccurrences(of: "\\n{2,}", with: "\n", options: .regularExpression) // squash runs of two or more newlines

or using a regular expression for the spaces:

let noHorizSpace = trimmedEnds.replacingOccurrences(of: " +", with: "", options: .regularExpression)
let singleVertSpace = noHorizSpace.replacingOccurrences(of: "\\n{2,}", with: "\n", options: .regularExpression)

But (for fun?) what about all Unicode horizontal (spaces, tabs, etc.) and vertical (newlines, form feeds, paragraph separators, etc.)? For that there are the RE patterns \h and \v:

let noHorizSpace = trimmedEnds.replacingOccurrences(of: "\\h+", with: "", options: .regularExpression)
let singleVertSpace = noHorizSpace.replacingOccurrences(of: "\\v+", with: "\n", options: .regularExpression)

You can solve this with a single regular expression, but it is better to heed the advice in ICU RE User Guide and use multiple simpler REs.