java - 如何获取新创建的文件中的月份总数？

Question

我目前正在研究C语言选项 3:下载统计数据

如果用户选择此选项，程序将创建一个包含以下数据的统计文件:

a.  Power output sorted from lowest to highest
b.  Day with highest output 
c.  Total by month 
d.  Average power output for all the data

统计文件将与输入文件同名，但附加 _stats.txt。例如，如果输入文件名为 data.txt，则统计文件将命名为 data_stats.txt。

我的数据文件包含

January 10 2018 236.9
January 11 2018 267.6
January 12 2018 278.1
January 13 2018 246.9
January 14 2018 262.3
January 15 2018 288.6
February 2 2018 199.7
February 3 2018 134.6
February 4 2018 200.8
February 5 2018 198.2
March 9 2018 169.7
March 10 2018 168.3
March 11 2018 179.4

当我运行C时，我的总功率是288.6，我如何获得每个月的总和？

 public static void createStatsFile(ArrayList<Entry> uploadResults) {
    ///////////////
    ///////A///////
    ///////////////
    try {
        PrintWriter writer = new PrintWriter("data_stat.txt", "UTF-8");

        ArrayList<Entry> lowestToHighest = bubbleSort(uploadResults);

        for(Entry entry : lowestToHighest) {
            writer.print(
                    "Month: " + entry.getMonth() + " Day: " + entry.getDay() + " Year: " + entry.getYear() + " Power Output: " + entry.getPowerOutput());
            writer.print("\n");
            entry.print();
        }

        ///////////////
        ///////B///////
        ///////////////
        Entry tmpEntry = null;

        for(Entry entry : uploadResults) {
            if(tmpEntry == null) {
                tmpEntry = entry;
            } else {
                if(entry.getPowerOutput() > tmpEntry.getPowerOutput()) {
                    tmpEntry = entry;
                }
            }
        }

        writer.write("Day of Max Power Outage: " + tmpEntry.getMonth() + " " + tmpEntry.getPowerOutput());

        ///////////////
        ///////C///////
        ///////////////

        //ArrayList<Entry> totalByMonth = bubbleSort(uploadResults);
        Entry tempEntry = null;
        for(Entry entry: uploadResults) {
            float sum;
            sum =entry.getPowerOutput();
        }

        writer.write("Total power output by month: " + tmpEntry.getMonthList() + " " + tmpEntry.getPowerOutput());
        writer.close();

我的类(class):

public class Entry {
    //declaring variables
    private String month;
    private String day;
    private String year;
    private float powerOutput;
    private String file;
    private int[] MonthList;
    String inputFile = file;

    //Constructors
    public Entry() {
    }

    public Entry(String m, String d, String y, float p) {
        month = m;
        day = d;
        year = y;
        powerOutput = p;
    }

    //creating print to call ArrayList in main
    public void print() {
        System.out.println("Month: " + month + " Day: " + day + " Year: " + year + " Power Output: " + powerOutput);
    }

    public static void getFile() {

    }

    public String getMonth() {
        return month;
    }

    public String getDay() {
        return day;
    }

    public String getYear() {
        return year;
    }

    public float getPowerOutput() {
        return powerOutput;
    }

    public int[] getMonthList() {
        return MonthList;
    }

    public String getInputFile() {
        return inputFile;
    }
}    

Answer 1

您可以使用流来获取所需结果的 Map。

 Map<String, Double> collect = uploadResults.stream().collect(
            Collectors.groupingBy(Entry::getMonth, Collectors.summingDouble(Entry::getPowerOutput)));

工作中

List<Entry> uploadResults = Arrays.asList(
        new Entry("January","10","2018",236.9f),
        new Entry("January","11","2018",267.6f),
        new Entry("January","12","2018",278.1f),
        new Entry("January","13","2018",246.9f),
        new Entry("January","14","2018",262.3f),
        new Entry("January","15","2018",288.6f),
        new Entry("February","2","2018",199.7f),
        new Entry("February","3","2018",134.6f),
        new Entry("February","4","2018",200.8f),
        new Entry("February","5","2018",198.2f),
        new Entry("March","9","2018",169.7f),
        new Entry("March","10","2018",168.3f),
        new Entry("March","11","2018",179.4f)
);

Map<String, Double> collect = uploadResults.stream().collect(
        Collectors.groupingBy(Entry::getMonth, Collectors.summingDouble(Entry::getPowerOutput)));

System.out.println(collect);

输出

{March=517.3999938964844, February=733.3000030517578, January=1580.3999938964844}

编辑:

对于 Java8 以下的版本，应该这样做

Map<String, Float> monthMap = new HashMap<>();
for (Entry uploadResult : uploadResults) {
    String month = uploadResult.getMonth();
    Float powerOutput = uploadResult.getPowerOutput();

    if( monthMap.containsKey(month) ){
        powerOutput += monthMap.get(month);
    }
    monthMap.put( month, powerOutput);
}
System.out.println(monthMap);