How to enter array objects into NSMutableArray?

Question

sortedArray contains 100+ objects that need to be organize by the 'hour' in the 'time' key. The outcome is to have an array of arrays to populate the sections of a table and use the hour for the index. 'time' is of the form - 2012-05-15 07:20:00

NSInteger d = 0;
NSInteger prevd;
NSMutableArray *tempArray = [[NSMutableArray alloc] init];
detailArray = [[NSMutableArray alloc] init];
for (NSInteger i = 0; i < 24; ++i)
    [detailArray addObject:[NSNull null]];

for (NSArray *item in sortedArray) {
    prevd = d;
    d = [[[[item objectAtIndex:0] objectForKey:@"time"] substringWithRange:NSMakeRange(11, 2)] intValue];
    if (d > prevd && prevd != 0) {
        [detailArray replaceObjectAtIndex:d withObject:tempArray];
        [tempArray removeAllObjects];
    }
    [tempArray addObject:item];
}

The objects are not ending up in the correct detailArray postition or not ending up in it at all. For instance, [detailArray objectAtIndex:6] give items with time 14 (2pm).

What am I missing?

Edit to correct code with 1st answer. It is now:

NSInteger d = 0;
NSInteger prevd;
NSMutableArray *tempArray = nil;
detailArray = [[NSMutableArray alloc] init];
for (NSInteger i = 0; i < 24; ++i)
    [detailArray addObject:[NSNull null]];

for (NSArray *item in sortedArray) {
    prevd = d;
    d = [[[[item objectAtIndex:0] objectForKey:@"time"] substringWithRange:NSMakeRange(11, 2)] intValue];
    if (d > prevd) {
        tempArray = NSMutableArray array];
        [detailArray replaceObjectAtIndex:d withObject:tempArray];
    }
    [tempArray addObject:item];
}

Answer 1

You can't reuse tempArray like that, you're going to end up with detailArray containing multiple entries that all point to the same tempArray instance. (i.e. every slot that had a time is going to end up with the array for the last time slot).

Instead of

[detailArray replaceObjectAtIndex:d withObject:tempArray];
[tempArray removeAllObjects];

you'll want

tempArray = [NSMutableArray array];
[detailArray replaceObjectAtIndex:d withObject:tempArray];

that way each time slot has its own array. And you'll also want to change your original declaration of tempArray to be

NSMutableArray *tempArray = nil;