我学会了如何使用可比对象,但是在使用比较器时遇到了困难。我的代码有错误: Exception in thread "main" java.lang.ClassCastException: New.People cannot be cast to java.lang.Comparable at java.util.Arrays.mergeSort(Unknown Source) at java.util.Arrays.sort(Unknown Source) at java.util.Collections.sort(Unknown Source) at New.TestPeople.main(TestPeople.java:18) 这是我的代码: import java.util.Comparator; public class People implements Comparator { private int id; private String info; private double price; public People(int newid, String newinfo, double newprice) { setid(newid); …
我想按两列对数据框进行分组,然后对各组中的汇总结果进行排序。 In [167]: df Out[167]: count job source 0 2 sales A 1 4 sales B 2 6 sales C 3 3 sales D 4 7 sales E 5 5 market A 6 3 market B 7 2 market C 8 4 market D 9 1 market E In [168]: …