How to split a string with newlines

问题

I read from a csv file, and want to split the long string that I get using stringWithContentsOfFile, which is a multi line string, with individual lines representing rows in the csv file. How do I do this?

回答1:

You can break the string into arrays of string and then manipulate as you want.

NSArray *brokenByLines=[yourString componentsSeparatedByString:@"\n"]

回答2:

Just in case anyone stumbles across this question like I did. This will work with any newline characters:

NSCharacterSet *separator = [NSCharacterSet newlineCharacterSet];
NSArray *rows = [yourString componentsSeparatedByCharactersInSet:separator];

回答3:

You should be aware that \n is not the only character used to split a new line. For example, if the file was saved in Windows, the newline characters would be \r\n. Read the Newline article in Wikipedia for more information about this.

Thus, if you just use componentsSeparatedByString("\n"), you may get unexpected results.

let multiLineString = "Line 1\r\nLine 2\r\nLine 3\r\n"
let lineArray = multiLineStringRN.componentsSeparatedByString("\n")
// ["Line 1\r", "Line 2\r", "Line 3\r", ""]

Note both the residual \r and the empty array element.

There are several ways to avoid these problems.

Solutions

1. componentsSeparatedByCharactersInSet

let multiLineString = "Line 1\nLine 2\r\nLine 3\n"
let newlineChars = NSCharacterSet.newlineCharacterSet()
let lineArray = multiLineString.componentsSeparatedByCharactersInSet(newlineChars).filter{!$0.isEmpty}
// "[Line 1, Line 2, Line 3]"

If filter were not used, then \r\n would produce an empty array element because it gets counted as two characters and so separates the string twice at the same location.

2. split

let multiLineString = "Line 1\nLine 2\r\nLine 3\n"
let newlineChars = NSCharacterSet.newlineCharacterSet()
let lineArray = multiLineString.utf16.split { newlineChars.characterIsMember($0) }.flatMap(String.init)
// "[Line 1, Line 2, Line 3]"

or

let multiLineString = "Line 1\nLine 2\r\nLine 3\n"
let lineArray = multiLineString.characters.split { $0 == "\n" || $0 == "\r\n" }.map(String.init)
// "[Line 1, Line 2, Line 3]"

Here \r\n gets counted as a single Swift character (an extended grapheme cluster)

3. enumerateLines

let multiLineString = "Line 1\nLine 2\r\nLine 3\n"
var lineArray = [String]()
multiLineString.enumerateLines { (line, stop) -> () in
    lineArray.append(line)
}
// "[Line 1, Line 2, Line 3]"

For more about the enumerateLine syntax, see this answer also.

Notes:

• a multi line string would not usually mix both \r\n and \n but I am doing this here to show that these methods can handle both formats.
• NSCharacterSet.newlineCharacterSet() are newline characters defined as (U+000A–U+000D, U+0085), which include \r and \n.
• This answer is a summary of the answers to my previous question. Read those answers for more detail.

回答4:

Swift 3 version:

let lines = yourString.components(separatedBy: .newlines)

Nice and short.

回答5:

You need to separate your content with "\n".

    NSString *str= [NSString stringWithContentsOfFile:filePathLib encoding:NSUTF8StringEncoding error:nil];
    NSArray *rows = [str componentsSeparatedByString:@"\n"];

    for(int i =0;i<[rows count];i++)
        NSLog(@"Row %d: %@",i,[rows objectAtIndex:i]);

回答6:

Here's my take on it:

    NSString* string = @"FOO\r\nBAR\r\r\n\rATZ\rELM327 v1.5";
    NSCharacterSet* newlineSet = [NSCharacterSet newlineCharacterSet];
    NSCharacterSet* whitespaceSet = [NSCharacterSet whitespaceAndNewlineCharacterSet];
    NSArray<NSString*>* components = [string componentsSeparatedByCharactersInSet:newlineSet];
    NSPredicate* predicate = [NSPredicate predicateWithBlock:^BOOL(NSString* _Nullable string, NSDictionary<NSString *,id> * _Nullable bindings){
        return [string stringByTrimmingCharactersInSet:whitespaceSet].length > 0;
    }];
    NSArray<NSString*>* lines = [components filteredArrayUsingPredicate:predicate];

    [lines enumerateObjectsUsingBlock:^(id  _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
        NSLog( @"Line %u = '%@'", idx, obj );
    }];

Running this prints:

2017-10-24 15:26:05.380 Untitled 5[64977:3182818] Line 0 = 'FOO'
2017-10-24 15:26:05.380 Untitled 5[64977:3182818] Line 1 = 'BAR'
2017-10-24 15:26:05.380 Untitled 5[64977:3182818] Line 2 = 'ATZ'
2017-10-24 15:26:05.380 Untitled 5[64977:3182818] Line 3 = 'ELM327 v1.5'

It may not be the most efficient way (probably using an NSScanner would be faster), but it solves the problem here.

来源：https://stackoverflow.com/questions/15156406/how-to-split-a-string-with-newlines