Sort Array By Sub-Array values in Objective C

I have a multi item array in Objective C where every item is a sub-array with 4 items.I need to sort the main array based on one of the values of the sub-array.

How can I do that (quickly)?

Array looks like this:

    (
    Marly,
    "Avenida Caracas - Calle 51",
    "4.637467,-74.066799",
    a,
    "10070.563466"
),
    (
    "开发者_C百科Calle 76",
    "Avenida Caracas - Calle 76",
    "4.662918,-74.061198",
    a,
    "7250.832506"
),
    (
    Profamilia,
    "Avenida Caracas - Calle 34",
    "4.621341,-74.06976",
    a,
    "11853.104432"
),
    (
    "Avenida 39",
    "Avenida Caracas - Calle 39",
    "4.626816,-74.068687",
    a,
    "11243.556349"
)

You can use any number of the NSArray or NSMutableArray sorting methods. If you're on iOS 4.0 or later, the most straightforward is probably the "UsingComparator:" version. That would go something like this:

[array sortUsingComparator:^NSComparisonResult(id a, id b) {
    NSString *name1 = [a objectAtIndex:0];
    NSString *name2 = [b objectAtIndex:0];
    return [name1 localizedCaseInsensitiveCompare:name2];
}]

nice code Anomie! exactly what i was looking for :)

but 2 things:

1 - it's "sortedArrayUsingComparator" the function for an NSArray not "sortUsingComparator"

2 - can you explain a bit the code:

^NSComparisonResult(id a, id b) {...}

like: what does the ^ does? from what i read from Apple Doc I assume what you did there was write a function to compare (the code between curly braces) and then typedef it to NSComparisonResult. but how come the objects (id a, id b) are assumed/used? is there a common way to do this for every function/data type?