如何從數組和/平均值/最小值/最大值中排除數字？

Question

我正在為班級分配作業，我試圖弄清楚如何獲取數組中數字的平均值，同時排除數字-999（用於指示缺少的數據），我想出了如何獲取總和/平均/最低/最高等，但我無法弄清楚如何從搜索范圍中排除-999。 您可以在前幾種方法中看到到目前為止我已經嘗試解決的一些事情。 我什至在Google上都找不到任何東西，甚至可能無法開始解釋我現在應該做什么。 這些是我要遵循的說明，以下是我當前的代碼，感謝您的輸入。

    /**
 * WeatherComputation.java
 */

//Put any imports below this line.
import java.util.*;

/**
 * Static methods library which compute averages and other
 * computations on integer arrays of temperatures.
 * 
 * @author Joel Swanson 
 * @version 03.29.2014
 */
public class WeatherComputation
{    
    /**
     * Average an array of temperatures.
     * @param temperatures An array storing temperatures as ints.
     * @return Returns the average of the array of ints.
     */
    public static double averageTemperature(int[] temperatures)
    {   
        int sum = 0;
        for (int i = 0; i < temperatures.length; i++)
        {
         sum += temperatures[i];
        }
        double average = sum / temperatures.length;
        return average;
    }

    /**
     * Find the highest in an array of temperatures.
     * @param temperatures An array storing temperatures as ints.
     * @return The largest value from the the array of ints.
     */
    public static int highestTemperature(int[] temperatures)
    {      
        int max = temperatures[0]; 
        for (int i = 1; i < temperatures.length; i++)
        {
            if(temperatures[i] > max)
            { 
                max = temperatures[i]; 
            } 
        }
        return max;
    } 

    /**
     * Find the lowest in an array of temperatures.
     * @param temperatures An array storing temperatures as ints.
     * @return The lowest value from the the array of ints.
     */
    public static int lowestTemperature(int[] temperatures)
    {
        int min = 0; 
        Arrays.sort(temperatures);

        while (true)
        {
            if (min == -999)
            {
                break;   
            }

            if(min > -999)
            {
                min = temperatures[0];
            }
        }

        for (int i = 1; i < temperatures.length; i++)
        {
            if (min < -999)
            {
                if (temperatures[i] < min)
                {
                    min = temperatures[i];   
                }    
            }
        } 

        return min;
    }

    /**
     * Return the total number of missing days.  That is days with
     * -999 recorded as the temperatures.
     * @param temperatures An array storing temperatures as ints.
     * @return The number of -999s found.
     */
    public static int numberMissing(int[] temperatures)
    {       
        int count = 0; 

        return count;
    } 

    /**
     * Calculate heating degree day.
     * @param max The highest temperature for a given day.
     * @param min The lowest temperature for a given day.
     * @return heating degree day data for this day.
     */
    public static double hdd(int max, int min)
    {
        double hdd = 0.0;

        return hdd;
    }

    /**
     * Calculate cooling degree day.
     * @param max The highest temperature for a given day.
     * @param min The lowest temperature for a given day.
     * @return cooling degree day data for this day.
     */
    public static double cdd(int max, int min)
    {
        double cdd = 0.0;

        return cdd;
    }    

    /**
     * Sum monthly heating degree days.
     * @param max An array with the highest temperatures for each day
     * in a given month.
     * @param min An array with the lowest temperatures for each day
     * in a given month.
     * @return The sum of the heating degree days.
     */
    public static double monthHdd(int[] max, int[] min)
    {
        double sum = 0.0;

        return sum;        
    }

    /**
     * Sum monthly cooling degree days.
     * @param max An array with the highest temperatures for each day
     * in a given month.
     * @param min An array with the lowest temperatures for each day
     * in a given month.
     * @return The sum of the cooling degree days.
     */
    public static double monthCdd(int[] max, int[] min)
    {
        double sum = 0.0;

        return sum;        
    }     
}

Answer 1

您確實想為此使用Java 8的流運算符。 如果我采用您的代碼，而忽略了未實現的方法，並且沒有描述實際計算的內容，那么我會得到：

/**
 * WeatherComputation.java
 */
import java.util.*;
import java.util.stream.IntStream;

/**
 * Static methods library which compute averages and other
 * computations on integer arrays of temperatures.
 *
 * @author Joel Swanson
 * @version 03.29.2014
 */
public class WeatherComputation {

    /**
     * Filters out all missing values (represented by -999).
     *
     * @param temperaturs an array storing temperatures as ints.
     * @return the list with the missing values removed
     */
    private static IntStream getFilteredArray(final int[] temperaturs) {
        return IntStream.of(temperaturs)
                .filter(i -> i != -999);
    }

    /**
     * Average an array of temperatures.
     *
     * @param temperatures an array storing temperatures as ints.
     * @return the average of the array of ints.
     */
    public static double averageTemperature(int[] temperatures) {
        // Returns 0 on an empty list. Your code will throw an exception
        return getFilteredArray(temperatures).average().orElse(0d);
    }

    /**
     * Find the highest in an array of temperatures.
     *
     * @param temperatures an array storing temperatures as ints.
     * @return the largest value from the the array of ints.
     */
    public static int highestTemperature(int[] temperatures) {
        return getFilteredArray(temperatures).max().orElse(0);
    }

    /**
     * Find the lowest in an array of temperatures.
     *
     * @param temperatures an array storing temperatures as ints.
     * @return the lowest value from the the array of ints.
     */
    public static int lowestTemperature(int[] temperatures) {
        return getFilteredArray(temperatures).min().orElse(0);
    }

    /**
     * Return the total number of missing days. That is days with
     * -999 recorded as the temperatures.
     *
     * @param temperatures an array storing temperatures as ints.
     * @return the number of -999s found.
     */
    public static int numberMissing(int[] temperatures) {
        return (int) IntStream.of(temperatures)
                .filter(t -> t == -999)
                .count();
    }
}

方法getFilteredArray完成所有工作。 它將數組轉換為IntStream ，刪除所有-999值，然后返回流。 然后，您可以使用流運算符來計算平均值，總和，最小值，最大值等值。

Answer 2

public static double averageTemperature(int[] temperatures)
    {   
        int sum = 0;
        int count = 0;// number of valid values
        for (int i = 0; i < temperatures.length; i++)
        {
            if(temperatures[i] > -999){ // before calculating check value
                  count ++;
                  sum += temperatures[i];
             }
        }
        double average = count != 0 ? sum / count : -999 - 1; // preventing divide by zero
        return average;
    }

public static int lowestTemperature(int[] temperatures) {
    if(temperatures == null || temperatures.length == 0)
        return -999 - 1;
    int min = temperatures[0];
    for (int temperature : temperatures) {
        if (temperature > -999 && temperature < min) {
            min = temperature;
        }
    }
    return min;
}

Answer 3

您只需要在每一步中檢查該值是否為排除值，然后再以sum / average / min / max方法使用它即可。

例如：

public static double averageTemperature(int[] temperatures) 
{   
    int sum = 0;
    int count = 0;
    for (int i = 0; i < temperatures.length; i++) 
    {
       if (temperatures[i] != -999) {
           sum += temperatures[i];
           count++;
       }
    }
    double average = sum / count;
    return average;
}

Answer 4

對於最低溫度，這就是我要做的：

public static int lowestTemperature(int[] temperatures) {
    int min = 999;
    for (int temperature : temperatures) {
        if (temperature > -999 && temperature < min) {
            min = temperature;
        }
    }
    return min;
}

假設您的WeatherComputation類也將考慮999的方式與考慮-999 （無效值）的方式相同。 原因很簡單，如果一個月內只有負值怎么辦？ 然后，您的int min = 0將是錯誤的。

至於平均溫度：

public static double averageTemperature(int[] temperatures) {
    int sum = 0, validTemperatureCounter = 0;
    for (int temperature : temperatures) {
        if (temperature > -999 && temperature < 999) {
            validTemperatureCounter++;
            sum += temperature;
        }
    }
    return sum / (double)validTemperatureCounter;
}

我也隨意忽略了999的值。

更新資料

為了好玩，有一個班輪：

public static double averageTemperatureOneLiner(int[] temperatures) {
    return Arrays.stream(temperatures).filter(t -> t > -999 && t < 999).average().orElse(0);
}


public static int lowestTemperatureOneLiner(int[] temperatures) {
    return Arrays.stream(temperatures).filter(t -> t > -999 && t < 999).min().orElse(0);
}


public static int highestTemperatureOneLiner(int[] temperatures) {
    return Arrays.stream(temperatures).filter(t -> t > -999 && t < 999).max().orElse(0);
}