如何使用for循环和Python中的csv库迭代列？

Question

我是一个非常新手的Python用户,试图在.csv文件中对数据列进行求和.我发现其他答案真正帮助我开始(例如这里和这里).

但是,我的问题是我想循环我的文件以获取所有列的总和.

我的格式化数据如下所示:

    z   y   x   w   v   u
a   0   8   7   6   0   5
b   0   0   5   4   0   3
c   0   2   3   4   0   3
d   0   6   7   8   0   9

或者像.csv格式一样:

,z,y,x,w,v,u
a,0,8,7,6,0,5
b,0,0,5,4,0,3
c,0,2,3,4,0,3
d,0,6,7,8,0,9

目前,我只是想让迭代工作.我会担心以后的总结.这是我的代码:

import csv
data = file("test.csv", "r")
headerrow = data.next()
headerrow = headerrow.strip().split(",")
end = len(headerrow)
for i in range (1, end):
    for row in csv.reader(data):
        print row[i]

这是我得到的:

>>> 
0
0
0
0
>>> 

因此,它为每行打印索引1处的值,但不会继续通过其他索引.

我在这里错过了什么明显的东西？

更新:

按照非常有用的建议和解释,我现在有这个:

import csv
with open("test.csv") as data:
    headerrow = next(data)
    delim = "," if "," == headerrow[0] else " "
    headerrow = filter(None, headerrow.rstrip().split(delim))
    reader = csv.reader(data, delimiter=delim, skipinitialspace=True)
    zipped = zip(*reader)
    print zipped
    strings = next(zipped)
    print ([sum(map(int,col)) for col in zipped])

这会返回一个错误:

Traceback (most recent call last):
  File "C:\Users\the hexarch\Desktop\remove_total_absences_test.py", line 9,     in <module>
    strings = next(zipped)
TypeError: list object is not an iterator

我不明白...？抱歉!

Answer 1

import csv
with  open('in.csv')as f:
    head = next(f)
    # decide delimiter by what is in header 
    delim = "," if "," ==  head[0] else " "
    # need to filter empty strings 
    head = filter(None, head.rstrip().split(delim))
    # skipinitialspace must be set as you have two spaces delimited
    reader = csv.reader(f,delimiter=delim, skipinitialspace=True)
    # transpose rows
    zipped = zip(*reader)
    # skip first column
    strings = next(zipped)
    # sum each column
    print([sum(map(int,col)) for col in zipped])

[0, 16, 22, 22, 0, 20]

要创建匹配标题与字母总和的字典,您可以这样:

print(dict(zip(list(head), (sum(map(int,col)) for col in zipped))))

哪个输出:

{'u': 20, 'w': 22, 'x': 22, 'z': 0, 'y': 16, 'v': 0}

我使用python3进行上述所有操作,如果你使用python2替换为:

zip -> itertools.izip
filter -> itertools.izip
map -> itertools.imap

Python 2代码:

import csv
from itertools import izip, imap, ifilter
with  open('in.csv')as f:
    head = next(f)
    # decide delimiter by what is in header
    delim = "," if "," ==  head[0] else " "
    # need to filter empty strings
    head = ifilter(None, head.rstrip().split(delim))
    # skipinitialspace must be set as you have two spaces delimited
    reader = csv.reader(f,delimiter=delim, skipinitialspace=True)
    # transpose rows
    zipped = izip(*reader)
    # skip first column
    strings = next(zipped)
    # sum each column
    print([sum(imap(int,col)) for col in zipped])

输出:

[0, 16, 22, 22, 0, 20]

如果你正在做很多这样的工作,那么pandas尤其是pandas.read_csv可能会有用,下面是一个非常基本的例子,一些熊猫大师可能希望添加到它:

import  pandas as pd

df = pd.read_csv("in.csv")
print(df.sum())
Unnamed: 0    abcd
z                0
y               16
x               22
w               22
v                0
u               20
dtype: object