Sort NSArray custom objects by another NSArray custom objects

Question

I have 2 different NSArray with custom objects as follows,

Item *item1 = [[Items alloc] init];
item1.number = @"1";
item1.serailNumber = @"S01";

Item *item2 = [[Items alloc] init];
item2.number = @"2";
item2.serailNumber = @"S02";

Item *item3 = [[Items alloc] init];
item3.number = @"3";
item3.serailNumber = @"S03";

Item *item4 = [[Items alloc] init];
item4.number = @"4";
item4.serailNumber = @"S04";

Item *item5 = [[Items alloc] init];
item5.number = @"5";
item5.serailNumber = @"S05";

NSArray *items = @[item1, item2, item3, item4, item5]; 

NSArray *specList = @[@{"number" : @"002", @"serialNumber" : @"S02"},
                     @{"number" : @"004", @"serialNumber" : @"S04"},
                     @{"number" : @"003", @"serialNumber" : @"S03"}];

Now I want to sort my items array based on specList array by comparing " number " property.

Now my expected items list is,

@[item2, item4, item3, item1, item5]

I have gone through several samples as listed below but I couldn't figure out how to compare with custom objects. Any help would be appreciated, Thanks in advance.

Sample 1 Sample 2

Answer 1

This should do the trick:

NSArray *sorted = [items sortedArrayUsingComparator:^NSComparisonResult(Item *item1, Item *item2) {
    NSInteger indexForItemEquivalent1InSpecList = [self indexForItem:item1 inList:specList];
    NSInteger indexForItemEquivalent2InSpecList = [self indexForItem:item2 inList:specList];
    return [@(indexForItemEquivalent1InSpecList) compare:@(indexForItemEquivalent2InSpecList)];
}];

NSLog(@"Sorted: %@", sorted);

With:

-(NSInteger)indexForItem:(Item *)item inList:(NSArray *)list
{
    for (NSInteger i = 0; i < [list count]; i++)
    {
        if ([list[i][@"number"] integerValue] == [[item number] integerValue])
        {
            return i;
        }
    }
    return NSIntegerMax; //If not found, we put it at the end of the list
}

Output:

Sorted: (
    "<Item 0x146678f0> number: 2 serial: S02",
    "<Item 0x14667e10> number: 4 serial: S04",
    "<Item 0x14667900> number: 3 serial: S03",
    "<Item 0x14654200> number: 1 serial: S01",
    "<Item 0x14667e20> number: 5 serial: S05"
)

I override -description to make log clearer:

-(NSString *)description
{
    return [NSString stringWithFormat:@"<%@ %p> number: %@ serial: %@", [self class], self, _number, _serailNumber];
}

In other words:
You have to find the index of the corresponding Item object inside specList (see indexForItem:inList: ). I used integerValue because you are using @"002" and @"2", which aren't equal strings.
Then in the NSComparator you compare the two indexes.

For item1 and item5 which are at the end, I let them as if. There is no guarantee of their order since they are not present in specList . If you want to put them in "ascending" order, you have to do instead:

NSInteger indexForItem1InSpecList = [self indexForItem:item1 inList:specList];
NSInteger indexForItem2InSpecList = [self indexForItem:item2 inList:specList];
if (indexForItem1InSpecList == NSIntegerMax && indexForItem2InSpecList == NSIntegerMax)
{
    return [@([[item1 number] integerValue]) compare:@([[item2 number] integerValue])];
}
else
{
    return [@(indexForItem1InSpecList) compare:@(indexForItem2InSpecList)];
}

Answer 2

Here is an example of sorting second array referring to the first one:

NSArray *users = @[@"Dave",@"Mike",@"Joe",@"Jason",@"Kevin"];
NSArray *iqs = @[@110,@145,@75,@122,@130];

NSMutableArray *array = [NSMutableArray array];
for (int idx = 0;idx<[users count];idx++) {
    NSDictionary *dict = @{@"Name": users[idx],@"IQ":iqs[idx]};
    [array addObject:dict];
}

NSSortDescriptor *descriptor = [NSSortDescriptor sortDescriptorWithKey:@"IQ" ascending:NO];
[array sortUsingDescriptors:@[descriptor]];