Merging dictionaries in Objective-C

Arrays and collections / Dictionaries

Dictionary initialization
Getting a value by key
Checking for a key
Adding and removing elements
Iterating over a dictionary
Number of elements
Default value
Getting a list of keys
Getting a list of values
Filtering elements
Getting keys by value
Sorting a dictionary by keys
Sorting a dictionary by values
Converting a dictionary
Merging dictionaries
Grouping a collection

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}