Python 向现有 csv 文件添加新列
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add a new column to an existing csv file
提问by user3641397
I have a csv file with 5 columns and I want to add data in a 6th column. The data I have is in an array.
我有一个包含 5 列的 csv 文件，我想在第 6 列中添加数据。我拥有的数据在一个数组中。
Right now, the code that I have will insert the data I would want in the 6th column only AFTER all the data that already exists in the csv file.
现在，只有在 csv 文件中已经存在的所有数据之后，我拥有的代码才会在第 6 列中插入我想要的数据。
For instance I have:
例如我有：
wind, site, date, time, value
10, 01, 01-01-2013, 00:00, 5.1
89.6 ---> this is the value I want to add in a 6th column but it puts it after all the data from the csv file
Here is the code I am using:
这是我正在使用的代码：
csvfile = 'filename'
with open(csvfile, 'a') as output:
writer = csv.writer(output, lineterminator='\n')
for val in data:
writer.writerow([val])
I thought using 'a'would append the data in a new column, but instead it just puts it after ('under') all the other data... I don't know what to do!
我认为 using'a'会将数据附加到一个新列中，但它只是将它放在（'under'）所有其他数据之后......我不知道该怎么做！
回答by Jonathan Eskritt
The append mode of opening files is meant to add data to the end of a file. what you need to do is provide random access to your file writing. you need to use the seek() method
打开文件的附加模式旨在将数据添加到文件的末尾。您需要做的是提供对文件写入的随机访问。你需要使用 seek() 方法
you can see and example here: http://www.tutorialspoint.com/python/file_seek.htm
你可以在这里看到和例子：http: //www.tutorialspoint.com/python/file_seek.htm
or read the python docs on it here: https://docs.python.org/2.4/lib/bltin-file-objects.htmlwhich isn't terribly useful
或者在这里阅读 python 文档：https: //docs.python.org/2.4/lib/bltin-file-objects.html这不是非常有用
if you want to add to the end of a column you may want to open the file read a line to figure out it's length then seek to the end.
如果您想添加到列的末尾，您可能需要打开文件读取一行以确定它的长度，然后寻找到末尾。
回答by Steven Rumbalski
Appending writes data to the end of a file, not to the end of each row.
追加将数据写入文件的末尾，而不是每行的末尾。
Instead, create a new file and append the new value to each row.
相反，创建一个新文件并将新值附加到每一行。
csvfile = 'filename'
with open(csvfile, 'r') as fin, open('new_'+csvfile, 'w') as fout:
reader = csv.reader(fin, newline='', lineterminator='\n')
writer = csv.writer(fout, newline='', lineterminator='\n')
if you_have_headers:
writer.writerow(next(reader) + [new_heading])
for row, val in zip(reader, data)
writer.writerow(row + [data])
On Python 2.x, remove the newline=''arguments and change the filemodes from 'r'and 'w'to 'rb'and 'wb', respectively.
在 Python 2.x 上，删除newline=''参数并将文件模式分别从'r'和更改'w'为'rb'和'wb'。
Once you are sure this is working correctly, you can replace the original file with the new one:
一旦您确定这正常工作，您可以用新文件替换原始文件：
import os
os.remove(csvfile) # not needed on unix
os.rename('new_'+csvfile, csvfile)
回答by fred.yu
csvmodule does not support writing or appending column. So the only thing you can do is: read from one file, append 6th column data, and write to another file. This shows as below:
csv模块不支持写入或附加列。所以你唯一能做的就是：从一个文件读取，附加第 6 列数据，然后写入另一个文件。这显示如下：
with open('in.txt') as fin, open('out.txt', 'w') as fout:
index = 0
for line in iter(fin.readline, ''):
fout.write(line.replace('\n', ', ' + str(data[index]) + '\n'))
index += 1
datais a intlist.
data是一个int列表。
I test these codes in python, it runs fine.
我在 python 中测试了这些代码，它运行良好。
