如何使用python csv阅读器查看B列中是否存在A列中的一行

Question

I have two columns in a csv file

ColumnA ColumnB
jon     don
eric    cathrine
don     sony
jay     jon
ron
anne

What I am trying to do is check if each value in columnA exist in ColumnB, in this case only 'jon' and 'don' exist in columnB I am using python and its csv reader, so far i have used the following code

with open('samplefile.csv', 'r') as csvfile:
    csvreader = csv.reader(csvfile, delimiter=',')
    for line in csvreader:
      if line[0] not in line[1]:
        print(line[0]+ " Does not exist")

this does not work because my code compares line by line instead of each value in columnA to any value in columnB I also tried throwing the values from csv into a list but that does work because it also appends empty values from columnB to the 2nd list. Any help is appreciated. I am not limited to csv reader I can use any other libraries like pandas.

Answer 1

Change your code like this:

with open('samplefile.csv', 'r') as csvfile:
    csvreader = csv.reader(csvfile, delimiter=',')
    second_column = [l[1] for l in csvreader]
    first_column = [l[0] for l in csvreader]
    for line in first_column:
      if line not in second_column:
        print(f"{line} Does not exist")

Answer 2

with pandas we can use .isin to return a boolean series:

df['check'] = df['ColumnA'].isin(df['ColumnB'])

print(df)
  ColumnA   ColumnB  check
0     jon       don   True
1    eric  cathrine  False
2     don      sony   True
3     jay       jon  False
4     ron      None  False
5    anne      None  False

Answer 3

You can do it with pandas:

#df from csv
df=pd.read_csv('samplefile.csv', header=0)
#iterate the df
for index, row in df.iterrows():
    if not row['ColumnA'].isin(df['ColumnB']) :
        print (f"{row['ColumnA']} doesn't exist")