Add up all values from an NSArray and find the average

Question

I'm using the following to get an output of:

    2013-06-06 11:44:27.325 [2570:907] Rating: 0
    2013-06-06 11:44:27.326 [2570:907] Rating: 2
    2013-06-06 11:44:27.327 [2570:907] Rating: 3 


[rateQuery findObjectsInBackgroundWithBlock:^(NSArray *rateObjects, NSError *error)
 {
     if( !error )
     {
         NSLog(@"rateobject %@", rateObjects);

         for (id item in rateObjects) {

             int ratingVal = [[item objectForKey:@"Rating"] intValue];
             NSLog(@"Rating: %d", ratingVal);
         }

     }
 }
 ];

I'm looking to add the numbers to get a total and then divide by a count to get an average "rating".

I tried this, but obviously the syntax is incorrect. I think I need to use an NSArray instead of "item":

NSNumber *sum=[[item objectForKey:@"Rating"] valueForKeyPath:@"@sum.floatValue"];
                 NSLog(@"Rating Sum: %@", sum);

thanks for any help.

This [question](http://stackoverflow.com/q/14398756/767730) seems very similar — Anupdas, Jun 06 '13 at 11:04

score 12 · Answer 1 · answered Jun 06 '13 at 11:06

You can get the average using KVC. An example

NSArray *objects = @[
@{ @"Rating": @4 },
@{ @"Rating": @6 },
@{ @"Rating": @10 }
];

NSLog(@"Average: %@", [objects valueForKeyPath:@"@avg.Rating"]);
// results in "Average: 6.666666"

So in your case use:

NSNumber *sum = [rateObjects valueForKeyPath:@"@sum.Rating"];
NSNumber *average = [rateObjects valueForKeyPath:@"@avg.Rating"];

DharaParekh · Accepted Answer · 2013-06-06T11:17:19.430

3

try this:

__block float sum = 0;
[rateQuery findObjectsInBackgroundWithBlock:^(NSArray *rateObjects, NSError *error)  {
    if( !error )      {
        NSLog(@"rateobject %@", rateObjects);

        for (id item in rateObjects) {
            sum = sum + [[item objectForKey:@"Rating"] intValue];
            int ratingVal = [[item objectForKey:@"Rating"] intValue];
            NSLog(@"Rating: %d", ratingVal);
        }
        NSLog(@"Sum: %f", sum);
        NSLog(@"Average: %f", sum/rateObjects.count);
    }
}];

edited Jun 06 '13 at 11:17

answered Jun 06 '13 at 11:04

DharaParekh

1,730
1
10
17

thanks! with this line sum = sum + [[item objectForKey:@"Rating"] intValue]; I get an error stating that "variable is not assignable (missing __block specific type specifier. Do I have to declare float sum in the .h file? thanks – hanumanDev Jun 06 '13 at 11:08

score 3 · Answer 3 · answered Jun 06 '13 at 11:06

3

Try this:

NSNumber *sum = [rateObjects valueForKeyPath:@"@sum.Rating"];

outside of your for-loop

answered Jun 06 '13 at 11:06

gasparuff

2,295
29
48

Add up all values from an NSArray and find the average

3 Answers3