How to group by the elements of an array in Objective C - ios

Question

As mentioned here is possible with swift to How to group by the elements of an array : How to group by the elements of an array in Swift using this extension :
public extension SequenceType {
/// Categorises elements of self into a dictionary, with the keys given by keyFunc
func categorise<U : Hashable>(#noescape keyFunc: Generator.Element -> U) -> [U:[Generator.Element]] {
var dict: [U:[Generator.Element]] = [:]
for el in self {
let key = keyFunc(el)
if case nil = dict[key]?.append(el) { dict[key] = [el] }
}
return dict
}
}
How to do the same with Objective C

Answer 1

Same results in Objective C. I tried this for your question and I got the solution now.It works fine.
NSArray *array = #[#{#"name" : #"lunch", #"date" : #"01-01-2015" , #"hours" : #"1"},
#{#"name" : #"dinner", #"date" : #"01-01-2015" , #"hours" : #"1"},
#{#"name" : #"dinner", #"date" : #"01-01-2015" , #"hours" : #"1"},
#{#"name" : #"lunch", #"date" : #"01-01-2015" , #"hours" : #"1"},
#{#"name" : #"dinner", #"date" : #"01-01-2015" , #"hours" : #"1"},
];
NSMutableArray *resultLunchArray = [NSMutableArray new];
NSMutableArray *resultDinnerArray = [NSMutableArray new];
NSMutableArray *finalResultsArray = [NSMutableArray new];
NSArray *groupLunch = [array valueForKeyPath:#"#distinctUnionOfObjects.name"];
for (NSString *str in groupLunch)
{
NSArray *groupNames = [array filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:#"name = %#", str]];
if([str isEqualToString:#"lunch"])
{
for (int i = 0; i < groupNames.count; i++)
{
NSString *nameLunch = [[groupNames objectAtIndex:i] objectForKey:#"name"];
NSString *dateLunch = [[groupNames objectAtIndex:i] objectForKey:#"date"];
NSString *strNameLunch = [NSString stringWithFormat:#"%# : %#",nameLunch,dateLunch];
[resultLunchArray addObject:strNameLunch];
}
[finalResultsArray addObject:resultLunchArray];
}
else{
for (int i = 0; i < groupNames.count; i++)
{
NSString *nameDinner = [[groupNames objectAtIndex:i] objectForKey:#"name"];
NSString *dateDinner = [[groupNames objectAtIndex:i] objectForKey:#"date"];
NSString *strNameDinner = [NSString stringWithFormat:#"%# : %#",nameDinner,dateDinner];
[resultDinnerArray addObject:strNameDinner];
}
[finalResultsArray addObject:resultDinnerArray];
}
}
NSLog(#"The final results are - %#",finalResultsArray);
The Output Reults are
The final results are - (
(
"lunch : 01-01-2015",
"lunch : 01-01-2015"
),
(
"dinner : 01-01-2015",
"dinner : 01-01-2015",
"dinner : 01-01-2015"
)
)