Objective-C Fast Enumeration: checking for BOOL

Question

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?

What is "TRUE booleans"? The question as posed is un-answerable. — zaph, Jul 27 '14 at 17:33

score 2 · Answer 1 · answered Jul 27 '14 at 17:37

2

If you have an array of dictionaries, and you want to filter them, then filteredArrayUsingPredicate: is the method to use.

You can create a predicate using the key from your dictionary (predicateWithFormat:).

This will then give you an array of dictionaries that match the conditions in your predicate.

No sample code, I'm answering this on a phone.

answered Jul 27 '14 at 17:37

jrturton

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Aight give me moment while I attempt this wizardry. – Tom Testicool Jul 27 '14 at 17:40
`NSPredicate` is good for readability and small arrays but fast-enumeration is actually faster. – Milo Jul 27 '14 at 18:08
I'd go for readability over performance every time, until I had a measurable, important performance problem. – jrturton Jul 27 '14 at 18:41

Milo · Accepted Answer · 2014-07-27T18:14:11.053

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.

Objective-C Fast Enumeration: checking for BOOL

2 Answers2