如何在 CSV 文件中对具有相同键的后续行进行分组

Question

如果 col1 等于之前行中的相同值，我正在尝试连接 col3，然后将输出写入新文件。我有一个如下所示的 CSV 文件：

col1,col2,col3
a,12,"hello "
a,13,"good day"
a,14,"nice weather"
b,1,"cat"
b,2,"dog and cat"
c,2,"animals are cute"

我想要的输出：

col1,col3
a,"hello good day nice weather"
b,"cat dog and cat"
c,"animals are cute"

这是我尝试过的：

import csv

with open('myfile.csv', 'rb') as inputfile, open('outputfile.csv','wb') as outputfile:
    reader=csv.reader(inputfile)
    writer=csv.writer(outputfile)
    next(reader)
    for row in reader:
        while row[0]==row[0]:
            concat_text=" ".join(row[2])
        print concat_text
        writer.writerow((row[0],concat_text))

它运行但我没有输出。帮助表示赞赏。

Answer 1

如果您对使用 pandas 感兴趣，可以将您的 DataFrame 分组，然后输出唯一值：

import pandas as pd

df = pd.read_csv('test.txt')
print(df)

您的原始数据帧

  col1  col2              col3
0    a    12            hello 
1    a    13          good day
2    a    14      nice weather
3    b     1               cat
4    b     2       dog and cat
5    c     2  animals are cute

第二个DataFrame

df2 = df.groupby(df['col1'])
df2 = df2['col3'].unique()
df2 = df2.reset_index()

print(df2)

将导致：

  col1                              col3
0    a  [hello , good day, nice weather]
1    b                [cat, dog and cat]
2    c                [animals are cute]

要连接第三列，您需要像这样使用apply：

df2['col3'] = df2['col3'].apply(lambda x: ' '.join(s.strip() for s in x))

  col1                          col3
0    a   hello good day nice weather
1    b               cat dog and cat
2    c              animals are cute

---

完整代码：

import pandas as pd

df = pd.read_csv('test.txt')
df2 = df.groupby(df['col1'])

df2 = df2['col3'].unique()
df2 = df2.reset_index()

df2['col3'] = df2['col3'].apply(lambda x: ' '.join(s.strip() for s in x))

df2.to_csv('output.csv')

Answer 2

import csv

with open('myfile.csv', 'rb') as inputfile, open('outputfile.csv', 'wb') as outputfile:
    reader=csv.reader(inputfile)
    writer=csv.writer(outputfile)
    prior_val = None
    text = []
    for line in reader:
        if line[0] == prior_val:
            text.append(line[2])
        else:
            if text:
                writer.writerow([prior_val, " ".join(text)])
            prior_val = line[0]
            text = [line[2]]
    if text:
        writer.writerow([prior_val, " ".join(text)])

>>> !cat outputfile.csv
col1,col3
a,hello  good day nice weather
b,cat dog and cat
c,animals are cute

>>> pd.read_csv('outputfile.csv', index_col=0)
                          col3
col1                              
a     hello  good day nice weather
b                  cat dog and cat
c                 animals are cute

Answer 3

问题是您将同一行与自身进行比较。此版本将最后一行与当前行进行比较。输出没有引号分隔，但它是正确的。 script.py的内容

#!/usr/bin/env python

import csv

with open('myfile.csv', 'rb') as inputfile, open('outputfile.csv','wb') as outputfile:
    reader=csv.reader(inputfile)
    writer=csv.writer(outputfile)
    next(reader)
    lastRow = None
    # assumes data is in order on first column
    for row in reader:
        if not lastRow:
            # start processing line with the first column and third column
            concat_text = row[2].strip()
            lastRow = row
            print concat_text
        else:
            if lastRow[0]==row[0]:
                # add to line
                concat_text = concat_text + ' ' + row[2].strip()
                print concat_text
            else:
                # end processing
                print concat_text
                writer.writerow((lastRow[0],concat_text))
                # start processing
                concat_text = row[2]
                print concat_text
            lastRow = row
    # write out last element
    print concat_text
    writer.writerow((lastRow[0],concat_text))

运行 ./script.py 后输出文件.csv 的内容

a,hello good day nice weather
b,cat dog and cat
c,animals are cute