如何比较和删除2 NSMutableArray中的公共对象（NSDictionaries）？

Question

I have two NSMutableArrays, filled with dictionary objects, like

NSMutableArray * bigArray = @[dictionary1,dictionary2,dictionary3];
NSMutableArray * smallArray = @[dictionary1];

I want to remove the common elements (dictionay1) from the big array

Note: small array is subset of big array and elements are distinct

Answer 1

[bigArray removeObjectsInArray:smallArray];

删除bigArray中包含的smallArray中的所有对象。

Answer 2

If each element is distinct (as you say in the comments) then you can filter the array using a predicate that removes all the objects that inside of the smaller subset. Since you are using an array in your question, I assume that the order of the objects matter.

If you need to preserve the order, then you will need to filter the array. Converting to a set will break the order (unless you are able to resort it afterwards.

You are using mutable arrays in your question, so I will do the same. Just be aware that the original array is actually modified:

NSMutableArray *original = [NSMutableArray arrayWithArray:@[@"A", @"E", @"C", @"B", @"D"]];
NSMutableArray *subset   = [NSMutableArray arrayWithArray:@[@"C", @"B"]];

NSLog(@"before : %@", original);

[original filterUsingPredicate:[NSPredicate predicateWithBlock:^BOOL(id evaluatedObject, NSDictionary *bindings) {
    // return YES for objects to keep
    return ![subset containsObject:evaluatedObject];
}]];

NSLog(@"after : %@", original);

The output of this code is:

before : (
    A,
    E,
    C,
    B,
    D
)
after : (
    A,
    E,
    D
)

You can see that the order is preserved.

---

If you don't want to modify the original array you can produce a new filtered array instead. The small difference is that you call filteredArrayUsingPredicate: instead of filterUsingPredicate: . The predicate is the same:

NSArray *filtered = [original filteredArrayUsingPredicate:[NSPredicate predicateWithBlock:^BOOL(id evaluatedObject, NSDictionary *bindings) {
    // return YES for objects to keep
    return ![subset containsObject:evaluatedObject];
}]];

Answer 3

NSSet is perfect class to do this kind of job. Try that;

NSMutableSet *bigSet = [NSMutableSet setWithArray:bigArray];
[bigSet minusSet:[NSMutableSet setWithArray:smallArray]];
bigArray = [[bigSet allObjects] mutableCopy];

The thing worth to point is that if your array will store duplicate and you convert it to NSSet the duplicate will be removed in that case you shouldn't use it. The second thing is it can change order of the elements in your array.