如何在csv文件中将一列乘以另一列并重新写入

Question

我有一些csv格式的数据，我需要将第三列乘以第六列并将结果附加到结尾。我的数据如下：

TITLE,TITLE,T,T,T,T 
data,data,5,data,data,98.7,data 
data,data,2,data,data,97,data 
data,data,5,data,data,98,data 
data,data,4,data,data,8.7,data 
data,data,5,data,data,9.7,data 
data,data,12.5,data,data,198.7,data 

我真正的新的编码，但我尝试如下：从收藏 导入CSV 进口日期时间 进口副本 导入defaultdict

class_col = 2 
data_col = 5 

with open('minitest.csv', 'r') as f: 
    data = [line.strip().split(',') for line in f] 

for row in data: 
    class_col*data_col 

with open('minitest_edit.csv', 'w') as nf: 
    nf.write('\n'.join(','.join(row) for row in data)) 

print "done" 

我没不会出现任何错误，有什么建议吗？由于OS”

Answer 1

这是如何更有效地做到这一点的方法，即通过不读取d ata在内存中，这将与更大的数据集有关：

import csv 
import tempfile 
import shutil 

input_file = 'minitest.csv' 

with open(input_file, 'rb') as f, \ 
    tempfile.NamedTemporaryFile(delete=False) as out_f: 

    # in order to be able to not have to read everything in memory, we have to 
    # write every processed row to disk immediatley; for that, we need a temporary 
    # file because we can't read and write a single file at the same time: 
    reader = csv.reader(f) 
    writer = csv.writer(out_f) 

    # header row 
    writer.writerow(next(reader)) 

    # note that this uses a generator not a list, so that writerows will lazily 
    # evaluate each row as it writes them to disk 
    writer.writerows(row + [float(row[2]) * float(row[5])] for row in reader) 

# one everything's done, overwrite the original file with the new contents. 
shutil.move(out_f.name, input_file) 

P.S.如果你只是没有写回到同一个文件中，它实际上会更简单 - 在处理代码完成之后，你总是可以手动执行移动，以便简化处理代码。

Answer 2

你想下面的繁殖栏位，并把它们添加到原有的：

new_data = [] 
for row in data: 
    new_data.append(row + [float(row[class_col]) * float(row[data_col])]) 

Answer 3

使用csv.reader和csv.writer：

import csv 


with open('minitest.csv', 'rb') as f: 
    reader = csv.reader(f) 
    data = [next(reader)] # title row 
    for row in reader: 
     data.append(row + [float(row[2]) * float(row[5])]) 

with open('minitest.csv', 'wb') as nf: 
    writer = csv.writer(nf) 
    writer.writerows(data) 

生产：

TITLE,TITLE,T,T,T,T 
data,data,5,data,data,98.7,data,493.5 
data,data,2,data,data,97,data,194.0 
data,data,5,data,data,98,data,490.0 
data,data,4,data,data,8.7,data,34.8 
data,data,5,data,data,9.7,data,48.5 
data,data,12.5,data,data,198.7,data,2483.75 

Answer 4

如果你是幸运的预设电台上LUNIX您可以使用AWK：

awk -F "\"*,\"*" '{print $0 "," $3*$6 }' test.csv > result.csv 

你可以使用Python http://docs.python.org/2/library/subprocess.html调用它。