NSPredicate that ignores whitespaces

Question

I need to use NSPredicate to match two strings, case-insensitive, diacritic insensitive, and whitespace-insensitive.

The predicate would look something like this:

[NSPredicate predicateWithFormat:@"Key ==[cdw] %@", userInputKey];

The 'w' modifier is an invented one to express what I'd like to use.

I can't just trim the userInputKey because the data-source "Key" values might have whitespaces in them too (they need those whitespaces, I can't just trim them beforehand).

For example, given a userInputKey "abc" the predicate should match all of

{"abc", "a b c", " a B    C   "}

and so on. Given a userInputKey"a B C" the predicate should also match all the values in the set above.

This can't be so hard to do, can it?

Nick Moore · Accepted Answer · 2012-04-10T12:55:31.723

How about defining something like this:

+ (NSPredicate *)myPredicateWithKey:(NSString *)userInputKey {
    return [NSPredicate predicateWithBlock:^BOOL(NSString *evaluatedString, NSDictionary *bindings) {
        // remove all whitespace from both strings
        NSString *strippedString=[[evaluatedString componentsSeparatedByCharactersInSet:[NSCharacterSet whitespaceCharacterSet]] componentsJoinedByString:@""];
        NSString *strippedKey=[[userInputKey componentsSeparatedByCharactersInSet:[NSCharacterSet whitespaceCharacterSet]] componentsJoinedByString:@""];
        return [strippedString caseInsensitiveCompare:strippedKey]==NSOrderedSame;
    }];
}

Then use it like this:

NSArray *testArray=[NSArray arrayWithObjects:@"abc", @"a bc", @"A B C", @"AB", @"a B d", @"A     bC", nil];
NSArray *filteredArray=[testArray filteredArrayUsingPredicate:[MyClass myPredicateWithKey:@"a B C"]];               
NSLog(@"filteredArray: %@", filteredArray);

The result is:

2012-04-10 13:32:11.978 Untitled 2[49613:707] filteredArray: (
    abc,
    "a bc",
    "A B C",
    "A     bC"
)

I had to lookup http://stackoverflow.com/questions/3543208/nsfetchrequest-and-predicatewithblock because I wanted to use the predicate with NSFetchRequest, but other than that, your solution worked beautifully. Thanks! — JiaYow, Apr 10 '12 at 13:20

score 2 · Answer 2 · edited Aug 10 '18 at 08:44

Swift 4:

func ignoreWhiteSpacesPredicate(id: String) -> NSPredicate {
    return NSPredicate(block: { (evel, binding) -> Bool in
        guard let str = evel as? String else {return false}
        let strippedString = str.components(separatedBy: CharacterSet.whitespaces).joined(separator: "")
        let strippedKey = id.components(separatedBy: CharacterSet.whitespaces).joined(separator: "")
        return strippedString.caseInsensitiveCompare(strippedKey) == ComparisonResult.orderedSame
    })
}

Example:

let testArray:NSArray =  ["abc", "a bc", "A B C", "AB", "a B d", "A     bC"]
let filteredArray = testArray.filtered(using: ignoreWhiteSpacesPredicate(id: "a B C"))

Result:

["abc", "a bc", "A B C", "A bC"]

NSPredicate that ignores whitespaces

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