Question

I am used to working in C# using the linq extensions (list.select(…).where(…) ext), and I was wondering if there was some way of doing the same sort of thing in Objective-C. This would save me from building a number of rather complicated queries using Core Data, which is great for some things, but perhaps not the best for complex queries (or maybe I’m just uninformed).

Is there some kind of equivalent for linq in Objective-C/Core Data?

EDIT: More specifically, I would like to count the number of elements that fit some criteria. Say my model has a field called date. I am trying to select the distinct dates, and then calculate how many of each date there are. In SQL this would be like a group by, and a COUNT aggregate.

Answer 1

Your question goes from very general (“linq equivalent?”) to very specific (computing count by date). I’ll just answer your specific question.

Unfortunately, NSArray doesn’t have a built-in map or select method, but it does offer NSCountedSet, which will compute what you want:

NSCountedSet *dateSet = [NSCountedSet set];
for (id thing in array) {
    [dateSet addObject:[thing date]];
}
for (NSDate *date in dateSet) {
    NSLog(@"There are %d instances of date %@", [dateSet countForObject:date], date);
}