Question

我有一个CSV，其中第6列表示该班级中学生人数的计数。我还有一段单独的代码，如果它们出现在不同的剧本中，会从课程中删除一些学生，我将如何重新计算每个班级的学生人数。请参阅以下示例数据：

Jan-20,Data,Class xpv,4,11yo+,4,more data....
Jan-20,Data,Class xpv,4,11yo+,4,more data....
Jan-20,Data,Class xpv,4,11yo+,4,more data....
Jan-20,Data,Class xpv,4,11yo+,4,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-50,Data,Class 22zn,2,10yo+,6,more data....
Jan-50,Data,Class 22zn,2,10yo+,6,more data....
Jan-50,Data,Class 22zn,2,10yo+,6,more data....
Jan-50,Data,Class 22zn,2,10yo+,6,more data....
Jan-50,Data,Class 22zn,2,10yo+,6,more data....
Jan-50,Data,Class 22zn,2,10yo+,6,more data....

标识要删除哪些行的列在“更多数据”中结束但是在删除任何一行时，如何编码以计算该类中剩余的学生数，主要是计数第2列并替换值第6列。（这些类名称都是唯一的）

我希望这是有道理的。感谢任何帮助！亲切的问候AEA

修改将上述数据保存为AEAtest.csv

我尝试运行以下代码：

import csv
import itertools
from operator import itemgetter
import random

def some_condition(line):
    return random.random() < 0.5 # delete lines randomly with 50% probability

def filter_data(data):
    for classname, group in itertools.groupby(data, itemgetter(2)):
        filtered_group = [line for line in group if some_condition(line)]
        new_sum = len(filtered_group)
        for line in filtered_group:
            line[5] = new_sum
            yield line

with open('C:\AEAtest.csv') as f_in, open('C:\AEAtest_MOD.csv', 'w') as f_out:
    reader = csv.reader(f_in)
    writer = csv.writer(f_out)
    writer.writerows(filter_data(reader))

输出如下：

Jan-20,Data,Class xpv,4,11yo+,2,more data....

Jan-20,Data,Class xpv,4,11yo+,2,more data....

Jan-30,Data,Class tn2,4,10yo+,7,more data....

Jan-30,Data,Class tn2,4,10yo+,7,more data....

Jan-30,Data,Class tn2,4,10yo+,7,more data....

Jan-30,Data,Class tn2,4,10yo+,7,more data....

Jan-30,Data,Class tn2,4,10yo+,7,more data....

Jan-30,Data,Class tn2,4,10yo+,7,more data....

Jan-30,Data,Class tn2,4,10yo+,7,more data....

Jan-50,Data,Class 22zn,2,10yo+,3,more data....

Jan-50,Data,Class 22zn,2,10yo+,3,more data....

Jan-50,Data,Class 22zn,2,10yo+,3,more data....

我想知道额外的线条现在是如何发生的，有趣的是上面的最后一行文字是第23行，接着是另外两行空白。

有关修复此错误的任何帮助？亲切的问候AEA

Answer 1

我认为你可以在你的csv数据上使用itertools.groupby，按类名分组。然后，当您遍历每个组时，如果已删除任何行，则可以更正计数。

from itertools import groupby
from operator import itemgetter

def filter_data(data):
    for classname, group in itertools.groupby(data, itemgetter(2)):
        filtered_group = [line for line in group if some_condition(line)]
        new_count = len(filtered_group)
        for line in filtered_group:
            line[5] = new_count
            yield line

给定some_condition函数，以下是如何使用它来打印过滤后的数据：

import csv
import random

def some_condition(line):
    return random.random() < 0.5 # delete lines randomly with 50% probability

data = """Jan-20,Data,Class xpv,4,11yo+,4,more data....
Jan-20,Data,Class xpv,4,11yo+,4,more data....
Jan-20,Data,Class xpv,4,11yo+,4,more data....
Jan-20,Data,Class xpv,4,11yo+,4,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-30,Data,Class tn2,4,10yo+,12,more data....
Jan-50,Data,Class 22zn,2,10yo+,6,more data....
Jan-50,Data,Class 22zn,2,10yo+,6,more data....
Jan-50,Data,Class 22zn,2,10yo+,6,more data....
Jan-50,Data,Class 22zn,2,10yo+,6,more data....
Jan-50,Data,Class 22zn,2,10yo+,6,more data....
Jan-50,Data,Class 22zn,2,10yo+,6,more data....""".splitlines()

for line in filter_data(csv.reader(data)):
    print(line)

您可能希望阅读和编写实际文件，而不是解析字符串并打印修改后的结果。这是一些（未经测试的）代码，显示了如何做到这一点：

with open('myfile.csv', 'rb') as f_in, open('myfile_filtered.csv', 'wb') as f_out:
    reader = csv.reader(f_in)
    writer = csv.writer(f_out)
    writer.writerows(filter_data(reader))

请注意，在Python 3中，文件应该以文本模式而不是二进制模式打开，但是您还需要传递额外的参数newline=""，以便让csv模块处理该行结局本身。

如何从读取csv重新计算每个类中的数字

1 个答案: