计算可变参数的移动平均值

Question

我有一个整数属性,每秒更新一次,信号强度值范围为0 - 100.

我希望能够在过去的10次,25次,50次测量中持续测量移动平均值.

这样做最有效的方法是什么？

我目前正在考虑使用NSMutableArray实现一组FIFO队列,并在每次在阵列具有必需条目数时在末尾添加新值时弹出前导值.但是,我不确定是否有更有效的方法来做到这一点.

Answer 1

我写了一个名为MovingAverage的简单类来处理这个问题.您使用要维护的周期数启动方法,并使用样本计数的模数跟踪其余部分,以了解要将其放入哪个静态槽.

初始化为

MovingAverage *avg5periods = [[MovingAverage alloc] initWithSize:5];

添加项目:

[avg5periods addSample:1.0];
NSLog(@"1.2f",[avg5periods movingAverage]); //1.0
[avg5periods addSample:2.0];
NSLog(@"1.2f",[avg5periods movingAverage]); //1.5
[avg5periods addSample:3.0];
NSLog(@"1.2f",[avg5periods movingAverage]); //2.0
[avg5periods addSample:4.0];
NSLog(@"1.2f",[avg5periods movingAverage]); //2.5
[avg5periods addSample:5.0];
NSLog(@"1.2f",[avg5periods movingAverage]); //3.0
[avg5periods addSample:6.0];
NSLog(@"1.2f",[avg5periods movingAverage]); //4.0

头文件:

#import <Foundation/Foundation.h>

@interface MovingAverage : NSObject {
    NSMutableArray *samples;
    int sampleCount;
    int averageSize;
}
-(id)initWithSize:(int)size;
-(void)addSample:(double)sample;
-(double)movingAverage;
@end

和实施文件:

#import "MovingAverage.h"

@implementation MovingAverage
-(id)initWithSize:(int)size {
    if (self = [super init]) {
        samples = [[NSMutableArray alloc] initWithCapacity:size];
        sampleCount = 0;
        averageSize = size;
    }
    return self;
}
-(void)addSample:(double)sample {
    int pos = fmodf(sampleCount++, (float)averageSize);
    [samples setObject:[NSNumber numberWithDouble:sample] atIndexedSubscript:pos];
}
-(double)movingAverage {
    return [[samples valueForKeyPath:@"@sum.doubleValue"] doubleValue]/(sampleCount > averageSize-1?averageSize:sampleCount);
}
@end