如何在python中删除行CSV [英] How to Delete Rows CSV in python

问题描述

我试图比较两个csv文件（fileA和fileB），并删除fileA中找不到fileB中的任何行。我想能够做到这一点，而不创建第三个文件。我想我可以使用csv writer模块，但现在我第二个猜测自己。

目前，我使用下面的代码来记录我的比较数据文件B：

  remove_list = set（）
 with open（'fileB'，'rb'）as file_b： 
 reader1 = csv.reader（file_b）
 next（reader1）
 for reader1：
 remove_list.add（（row [0]，row [2]））
  

这是我被卡住的地方，不知道如何删除这些行：

 与open（'fileA'，'ab'）as file_a：
 with open（'fileB'，'rb'）as file_b ：
 writer = csv.writer（file_a）
 reader2 = csv.reader（file_b）
 next（reader2）
对于reader2中的行：
 if（row [ 0]，row [2]）不在remove_list中：
＃如果行不存在于文件B中，则从文件A中删除它。
 #stuck here：writer。< HowDoIRemoveRow>此解决方案使用
   docs.python.org/2/library/fileinput.html>  fileinput    inplace = True  ，它写入一个临时文件，然后自动将其重命名到文件名的末尾。您不能从文件中删除行，但只能使用您想要的行重写。
 
 
如果将 inplace = 1 的关键字参数传递给 fileinput.input（）或 FileInput 构造函数，文件被移动到备份文件，标准输出被定向到输入文件（如果与备份文件同名的文件已经存在，它将被静默替换）。 
 
 
 fileA 
  h1，h2，h3 
a，b，c 
d，e，f 
g，h，i 
j，k， l 
  
 fileB 
  h1，h2，h3 
a，b，c 
 1,2,3 
g，h，i 
 4,5,6 
  
 
 
 
 
 
 
  import fileinput，sys，csv 
 
 with open（'fileB'，'rb'）as file_b：
r = csv.reader（file_b）
 next（r）#skip header 
 seen = { （row [0]，row [2]）for row in r} 
 
f = fileinput.input（'fileA'，i​​nplace = True）＃sys.stdout重定向到文件
打印next（f），＃写头作为第一行
 
w = csv.writer（sys.stdout）
对于csv.reader（f）中的行：
 if [0]，row [2]）in：see如果它在B中则写入
 w.writerow（row）
  
 
 
 
 
 
 
 fileA 
  h1，h2，h3 
a，b，c 
g，h，i 
  
 
I'm trying to compare two csv files (fileA and fileB), and remove any rows from fileA that are not found in fileB.  I want to be able to do this without creating a third file.  I thought I could do this using the csv writer module but now I'm second guessing myself.

Currently, I'm using the following code to record my comparison data from file B:
removal_list = set()
with open('fileB', 'rb') as file_b:
    reader1 = csv.reader(file_b)
    next(reader1)
    for row in reader1:
        removal_list.add((row[0], row[2]))
This is where I'm stuck and do not know how to delete the rows:
with open('fileA', 'ab') as file_a:
    with open('fileB', 'rb') as file_b:
        writer = csv.writer(file_a)
            reader2 = csv.reader(file_b)
            next(reader2)
            for row in reader2:
                if (row[0], row[2]) not in removal_list:
                # If row was not present in file B, Delete it from file A.
                #stuck here:  writer.<HowDoIRemoveRow>(row)

解决方案
This solution uses fileinput with inplace=True, which writes to a temporary file and then automatically renames it at the end to your file name. You can't remove rows from a file but you can rewrite it with only the ones you want.

  
if the keyword argument inplace=1 is passed to fileinput.input() or to the FileInput constructor, the file is moved to a backup file and standard output is directed to the input file (if a file of the same name as the backup file already exists, it will be replaced silently). This makes it possible to write a filter that rewrites its input file in place.
fileA
h1,h2,h3
a,b,c
d,e,f
g,h,i
j,k,l
fileB
h1,h2,h3
a,b,c
1,2,3
g,h,i
4,5,6




import fileinput, sys, csv

with open('fileB', 'rb') as file_b:
    r = csv.reader(file_b)
    next(r) #skip header
    seen = {(row[0], row[2]) for row in r}

f = fileinput.input('fileA', inplace=True) # sys.stdout is redirected to the file
print next(f), # write header as first line

w = csv.writer(sys.stdout) 
for row in csv.reader(f):
   if (row[0], row[2]) in seen: # write it if it's in B
       w.writerow(row)




fileA
h1,h2,h3
a,b,c    
g,h,i


                        
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