ios - 计算数组中的平均值

Question

我需要在我的应用程序中添加一些东西来计算一组数字的平均值。

如果我有 3 个数字：10、20 和 30，我如何取数组中的所有数字，将它们加在一起 ​​(60)，然后除以总数并将最终数字呈现在某个地方，就像一个标签？

Answer 1

In addition to katzenhut's suggestion of manually calculating the average, you can use KVC collection operators, too, e.g.:

NSArray *array = @[@10, @25, @30];

NSNumber *average = [array valueForKeyPath:@"@avg.self"];

Or, if dealing with objects, for example a "Product" model object with this interface:

@interface Product : NSObject

@property (nonatomic, copy) NSString *name;
@property (nonatomic) double price;

- (id)initWithName:(NSString *)name price:(double)price; // the corresponding implementation should be obvious, so I'll not include it in this code snippet

@end

You could then do:

NSMutableArray *products = [NSMutableArray array];
[products addObject:[[Product alloc] initWithName:@"item A" price:1010.0]];
[products addObject:[[Product alloc] initWithName:@"item B" price:1025.0]];
[products addObject:[[Product alloc] initWithName:@"item C" price:1030.0]];

NSNumber *average = [products valueForKeyPath:@"@avg.price"];

---

If you want to take the results and populate a label with the results, you might do something like:

NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
formatter.numberStyle = NSNumberFormatterDecimalStyle;
formatter.maximumFractionDigits = 2;                   // two decimal places?

self.averageLabel.text = [formatter stringFromNumber:average];

The advantage of NSNumberFormatter over stringWithFormat is that you have greater control over the string representation of the number, e.g. it can observe localization, employ thousandths separators, etc.

Answer 2

您应该有一个包含单元格值的数组，并且您应该在编辑单元格时更新该数组。因此，将这些值加起来以备后用（例如，在名为 的浮点数中total）。

float total;
total = 0;
for(NSNumber *value in myArray){
    total+=[value floatValue];
}

将总数除以计数，您就完成了。喜欢float average = total/myArray.count

Answer 3

你应该有一个合适的数据模型。例如，如果您有 30 个单元格，则无需在表格视图中显示所有 30 个单元格。这样做会浪费资源，这也是为什么我们总是在 tableview 委托中实现 dequereuseable 方法的原因。

话虽如此，做这样的事情

#import <UIKit/UIKit.h>

@interface ViewController : UITableViewController

@end

实现如下

 #import "ViewController.h"

@interface ViewController ()
{
    NSArray *numbersList;
}

-(float) calculateAvg;

@end

@implementation ViewController

- (id)initWithStyle:(UITableViewStyle)style
   {
    self = [super initWithStyle:style];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    numbersList = [[NSArray alloc]initWithObjects:@"10",@"23",@"34",@"43",@"57",@"64",@"77",@"88",@"95",nil];
    [[self tableView] setDelegate:self];
    [[self tableView] setDataSource:self];
}

#pragma mark - 表格视图数据源

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    // Return the number of sections.
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    // Return the number of rows in the section. Plus one to hold average
    return [numbersList count] + 1;
}

 - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"cell"];

    if(cell == nil)
    {
        cell = [[UITableViewCell alloc]initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"cell"];
    }

    if([indexPath row] < [numbersList count])
    {
        [[cell textLabel] setText:[numbersList objectAtIndex:[indexPath row]]];
    }
    else
    {
        float avg = [self calculateAvg];
        [[cell textLabel] setText:[NSString stringWithFormat:@"%f",avg]];
    }


    return cell;

}

-(float) calculateAvg
{
    float avg = 0;

    for(int idx=0;idx<[numbersList count];idx++)
    {
        int tempValue = [[numbersList objectAtIndex:idx] intValue];
        avg = avg + tempValue;
    }

    return (avg / [numbersList count]);
}