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objective-cxcodefast-enumeration

Objective-C Fast Enumeration: checking for BOOL

Scenario = I need to loop through an array and find how many "unread" there are and count how many to display to the user.

What I'm Looking For = something like this (this is not my real code)

for (NSDictionary *dic in self.objects) {

    [unreadCountArray addObject:dic[@"wasRead"]];

    for (YES in unreadCountArray) {

        //statements

    }
}

Question = Does anyone know how to loop through and find all of the YES booleans?

Solution 
  • NSPredicate *predicate = [NSPredicate predicateWithFormat:@"wasRead = YES"];
NSArray *arr = [array filteredArrayUsingPredicate:predicate];

    Can sort a thousand objects in 0.0004 seconds.

    Then just do:

    for (NSDictionary *object in arr) {
    //Statements
}

    Edit: actually after further experimentation, using fast-enumeration is about four times faster, about 0.0001, which if scaled to 100000 objects can be much, much faster.

    NSMutableArray *test = [NSMutableArray array];

for (NSDictionary *dict in array)
    if ([dict[@"theKey"] boolValue])
        [test addObject:dict];

    So for sorting, fast-enumeration is actually faster but for just a couple hundred objects, the performance increase is negligible.

    And please before asking questions like this and getting downvotes, those could have been completely avoided by checking the documentation. Like this article and this article.