Take average of segments of NSArray

Question

I have an NSArray of 100 numbers. I would like to create an NSArray of 5 numbers. The first number in the second array is the average of the first 20 numbers in the first array. The second number is the average of the second set of 20 numbers in the first array. And so on.

I'm curious to hear people's ideas for an efficient algorithm.

One idea I had was to do a for-loop on each set of 20 numbers, creating a temp NSArray of 20 numbers. Then perform a KVO average operation and add to the final NSArray.

Note: I always award THE answer to someone, and I'm not shy to up vote your answers. I encourage many answers. Thanks!

Answer 1

The following is simple and efficient:

NSArray *numbers = ... // array of 100 numbers
NSMutableArray *averages = [NSMutableArray array];

for (int = 0; i < 5; i++) {
    float total = 0.0;
    int base = i * 20;
    for (int j = 0; j < 20; j++) {
        float num = [numbers[base + j] floatValue];
        total += num;
    }

    float avg = total / 20.0f;
    [averages addObject:@(avg)];
}

NSLog(@"Averages = %@", averages);