如何解决 NaN 错误

Question

这是计算平均值的代码，当我运行我的项目时出现 NaN 错误

public  static double calculateAverage(){
    double attendence = 0;
    int no_of_matches = 0;
    double average =0;
        for (Team t: ApplicationModel.getTeamList()){
        for(Match m : ApplicationModel.getMatchList()){
                if(m.getTeamname().equals(t.getName())){
                    attendence =+ (m.getAttendence());
                    no_of_matches ++;   
                }
            }
            average = attendence / no_of_matches ;
    } 
        return average;
}

这是调用计算平均值方法的代码

String[] columnNames = {"Name","Coaches","League","Division","Fulltime","Number of Coaches","Average Attendence"};

 if (ApplicationModel.getTeamList()!=null){
     int arrayIndex=0;
     for (Team c :ApplicationModel.getTeamList()){
           String[] currentRow = new String[7];
           currentRow[0] = c.getNameAsString();
           currentRow[1] = c.getCoachesAsString();
           currentRow[2] = c.getLeague();
           currentRow[3] = c.getDivision();
           currentRow[4] = c.getFulltime();
           currentRow[5] = Integer.toString(c.getCoaches().length);
           currentRow[6] = Double.toString(c.calculateAverage());
           rowInfo[arrayIndex]=currentRow;
           arrayIndex++;
           teamDisplay.append(c.toString());
         }
        }

Answer 1

我认为问题可能出在这行代码上：

attendence =+ (m.getAttendence());

不是将值添加到总变量，而是将总变量分配给值。另一个问题是您没有处理no_of_matches（根据命名约定，这是一个糟糕的变量名）为0 的情况，即没有匹配项。最后，average = attendence / no_of_matches 总是重新分配average，从而丢弃之前团队的任何结果。

代码建议：

double attendence = 0;
int matches = 0;
for (Team t: ApplicationModel.getTeamList())
{
    for(Match m : ApplicationModel.getMatchList())
    {
        if(m.getTeamname().equals(t.getName()))
        {
            attendence += (m.getAttendence());
            matches++;
        }
    }
} 
return matches > 0 ? attendence / matches : 0D;

Answer 2

我认为你可以在除法操作中使用之前修复 NAN 错误检查 if no_of_matches > 0。

public static double calculateAverage(){
    double attendence = 0;
    int no_of_matches = 0;
    double average = 0;

    for (Team t: ApplicationModel.getTeamList()) {
        for (Match m: ApplicationModel.getMatchList()) {
            if (m.getTeamname().equals(t.getName())) {
                attendence =+ (m.getAttendence());
                no_of_matches ++;   
            }
        }

        if (no_of_matches > 0)
            average = attendence / no_of_matches ;
    }

    return average;
}

附加说明，当您添加此检查并且 no_of_matches 是 0 时，您的平均值将为 0，这意味着您没有匹配项。

希望这会有所帮助。