仅当有对象时才进行连接

Question

我有一个从包含学生 ID、姓名和作业 1、2、3 的 csv 文件构建的数据框... csv 文件将作为输入输入，因此值可能会有所不同。如果学生 ID 不唯一，我想打印错误消息列表。下面的代码工作正常，因为 GradesM3.csv 中没有重复项：        grades = pd.read_csv('gradesM3.csv',sep=';')        duplicates = pd.concat(g for _, g in grades.groupby("StudentID") if len(g) > 1)              zipped = zip(duplicates['StudentID'])        for student in zipped:            print(f'The student ID {student} appears multiple times.')但是，如果我更改 CSV 文件并创建一些重复的学生 ID，则会出现以下错误：ValueError: No objects to concatenate如果有重复，我正在尝试编写一个打印以下内容的代码：The student ID ('s123789',) appears multiple times.The student ID ('s123789',) appears multiple times.The student ID ('s123789',) appears multiple times.如果没有，则如下：There are no duplicates in your file. 我尝试了以下代码：        grades = pd.read_csv('gradesM3.csv',sep=';')        duplicates = pd.concat(g for _, g in grades.groupby("StudentID") if len(g) > 1)         if len(duplicates)>0:            zipped = zip(duplicates['StudentID'])            for student in zipped:                print(f'The student ID {student} appears multiple times.')        else:            print('The grades are correctly scaled along the 7-point grading system.')但我收到相同的错误消息：ValueError: No objects to concatenate. 在此先感谢您的帮助。

Answer 1

使用duplicatedpandas的方法更直接的解决方案是这样的

import pandas as pd

# Example data

df = pd.DataFrame({'id' : [1,2,2,4, 5, 1], 'name' : ["a", "b", "b", "d", "e", "a"]})

print(df)

#   id name

#0   1    a

#1   2    b

#2   2    b

#3   4    d

#4   5    e

#5   1    a

# Get the duplicates - each df row where th eid column is duplicated

df_duplicates  = df[df['id'].duplicated()]

for id in df_duplicates['id']:

    print(f"Student {id} is a duplicate")

#Student 2 is a duplicate

#Student 1 is a duplicate