How to sort NSMutableArray elements? - iphone

Question

I have model class which contains NSString's- studentName, studentRank and studentImage. I wanna sort the NSMutableArray according to studentRanks. what I have done is
- (void)uploadFinished:(ASIHTTPRequest *)theRequest
{
NSString *response = nil;
response = [formDataRequest responseString];
NSError *jsonError = nil;
SBJsonParser *json = [[SBJsonParser new] autorelease];
NSArray *arrResponse = (NSArray *)[json objectWithString:response error:&jsonError];
if ([jsonError code]==0) {
// get the array of "results" from the feed and cast to NSArray
NSMutableArray *localObjects = [[[NSMutableArray alloc] init] autorelease];
// loop over all the results objects and print their names
int ndx;
for (ndx = 0; ndx < arrResponse.count; ndx++)
{
[localObjects addObject:(NSDictionary *)[arrResponse objectAtIndex:ndx]];
}
for (int x=0; x<[localObjects count]; x++)
{
TopStudents *object = [[[TopStudents alloc] initWithjsonResultDictionary:[localObjects objectAtIndex:x]] autorelease];
[localObjects replaceObjectAtIndex:x withObject:object];
}
topStudentsArray = [[NSMutableArray alloc] initWithArray:localObjects];
}
}
How can I sort this topStudentsArray according to the ranks scored by the Students and If the two or more student have the same rank, How can I group them.
I did like this
TopStudents *object;
NSSortDescriptor * sortByRank = [[[NSSortDescriptor alloc] initWithKey:#"studentRank" ascending:NO] autorelease];
NSArray * descriptors = [NSArray arrayWithObject:sortByRank];
NSArray * sorted = [topStudentsArray sortedArrayUsingDescriptors:descriptors];
but this is not displaying results properly. please help me to overcome this problem. thanks in advance.

Answer 1

doing something like this might do the trick
Initially sort the arrGroupedStudents in the (ascending/descending) order of studentRank
//Create an array to hold groups
NSMutableArray* arrGroupedStudents = [[NSMutableArray alloc] initWithCapacity:[topStudentsArray count]];
for (int i = 0; i < [topStudentsArray count]; i++)
{
//Grab first student
TopStudents* firstStudent = [topStudentsArray objectAtIndex:i];
//Create an array and add first student in this array
NSMutableArray* currentGroupArray = [[[NSMutableArray alloc] initWithCapacity:0] autorelease];
[currentGroupArray addObject:firstStudent];
//create a Flag and set to NO
BOOL flag = NO;
for (int j = i+1; j < [topStudentsArray count]; j++)
{
//Grab next student
TopStudents* nextStudent = [topStudentsArray objectAtIndex:j];
//Compare the ranks
if ([firstStudent.studentRank intValue] == [nextStudent.studentRank intValue])
{
//if they match add this to same group
[currentGroupArray addObject:nextStudent];
}
else {
//we have got our group so stop next iterations
[arrGroupedStudents addObject:currentGroupArray];
// We will assign j-1 to i
i=j-1;
flag = YES;
break;
}
}
//if entire array has students with same rank we need to add it to grouped array in the end
if (!flag) {
[arrGroupedStudents addObject:currentGroupArray];
}
}
Finally your arrGroupedStudents will contain grouped array with equal rank. I have not test run the code so you might need to fix a few things falling out of place. Hope it helps

Answer 2

If you want to display in the order of ranks, you should set the ascending as YES.
NSSortDescriptor * sortByRank = [[NSSortDescriptor alloc] initWithKey:#"studentRank" ascending:YES];

Answer 3

static int mySortFunc(NSDictionary *dico1, NSDictionary *dico2, void *context)
{
NSString *studentName1 = [dico1 objectForKey:#"studentName"];
NSString *studentName2 = [dico2 objectForKey:#"studentName"];
return [studentName1 compare:studentName2];
}
- (IBAction)sortBtnTouched:(id)sender
{
[topStudentsArray sortUsingFunction:mySortFunc context:NULL];
}