NSDictionary *d1 = @{@1: @"one"};
NSDictionary *d2 = @{@2: @"two",
                     @3: @"three"};

//copy of the first, then merge
NSMutableDictionary *dAll =
    [NSMutableDictionary
        dictionaryWithDictionary:d1];
[dAll addEntriesFromDictionary:d2];
//dAll is {1: one, 2: two, 3: three}