Sorting negative and positive numbers in objective

问题:

I am listing out a quantity percentage like stuff for an item via a webservice.The response that I get is an array of dictionaries similar to the below code.I need it in a sorted format

NSArray *numberArray = [NSArray arrayWithObjects:
    [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithFloat:-12.0], @"price", nil],
    [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithFloat:-86.0],@"price", nil],
    [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithFloat:-8.0],@"price", nil],
    [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithFloat:12.0],@"price", nil],
    [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithFloat:2.0],@"price", nil],
    [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithFloat:112.0],@"price", nil], nil];

Here's the log of the JSON response

[
    {
        price = "-12";
    },
        {
        price = "-86";
    },
        {
        price = "-8";
    },
        {
        price = 12;
    },
        {
        price = 2;
    },
        {
        price = 112;
    }
]

回答1:

NSArray *sortedResult = [numberArray sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
    NSNumber *num1 = [obj1 objectForKey:@"price"];
    NSNumber *num2 = [obj2 objectForKey:@"price"];
    return [num1 compare:num2];
}];
NSLog(@"---%@",sortedResult);

If you want the sortedResult in descending order then interchange the num1 and num2 in
return statement.

回答2:

If the prices are stored as NSNumber objects, then the method from @trojanfoe's link (Best way to sort an NSArray of NSDictionary objects?) should work:

NSSortDescriptor *sd = [NSSortDescriptor sortDescriptorWithKey:@"price" ascending:YES];
NSArray *sorted = [numberArray sortedArrayUsingDescriptors:@[sd]];

But from your last comment it seems that the prices are stored as strings. In that case the following works, because floatValue converts each string to a floating point value:

NSSortDescriptor *sd = [NSSortDescriptor sortDescriptorWithKey:@"price.floatValue" ascending:YES];
NSArray *sorted = [numberArray sortedArrayUsingDescriptors:@[sd]];

回答3:

You are not sorting numbers. You are sorting dictionaries, according to a common "price" element:

sortedArray = [numberArray sortedArrayUsingComparator:^NSComparisonResult(NSDictionary *a, NSDictionary *b) {
    return [a[@"price"] compare:b[@"price"]];
}];

回答4:

sortedArray = [numberArray sortedArrayUsingComparator:^NSComparisonResult(id a, id b) {
    float first  = [(NSNumber *)a[@"price"] floatValue];
    float second = [(NSNumber *)b[@"price"] floatValue];

    if (first > second) {
        return NSOrderedDescending;
    } else if (first < second) {
        return NSOrderedAscending;
    }

    return NSOrderedSame;
}];