python - python获取csv文件中一列的另一列的值

Question

我的 csv 文件如下:

ID        Value      Amount 
----      -------    -------
A           3          2
A           4          4
B           3          6
C           5          5
A           3          2
B           10         1

我想要“ID”列“值”或“金额”列的总和。我想要的输出是，对于“A”，它应该给出与 A 相关的所有值的总和，即 [3+4+3]。

我的代码:

import csv
file = open(datafile.csv)
rows=csv.DictReader(file)
summ=0.0
count=0
for r in rows:
  summ=summ+int(r['Value'])
  count=count+1
print "Mean for column Value is: ",(summ/count)
file.close()

Answer 1

您可以使用 list 的 defaultdict 按 ID 列对数据进行分组。然后使用 sum() 生成总计。

from collections import defaultdict

with open('datafile.csv') as f:
    d = defaultdict(list)
    next(f)    # skip first header line
    next(f)    # skip second header line
    for line in f:
        id_, value, amount = line.split()
        d[id_].append((int(value), int(amount)))

# sum and average of column Value by ID
for id_ in d:
    total = sum(t[0] for t in d[id_])
    average = total / float(len(d[id_]))
    print('{}: sum = {}, avg = {:.2f}'.format(id_, total, average))

输入数据的输出:

A: sum = 10, avg = 3.33C: sum = 5, avg = 5.00B: sum = 13, avg = 6.50

---

It can also be done with a standard Python dictionary. The solution is very similar:

with open('datafile.csv') as f:
    d = {}
    next(f)    # skip first header line
    next(f)    # skip second header line
    for line in f:
        id_, value, amount = line.split()
        d[id_] = d.get(id_, []) + [(int(value), int(amount))]

# sum and average of column Value by ID
for id_ in d:
    total = sum(t[0] for t in d[id_])
    average = total / float(len(d[id_]))
    print('{}: sum = {}, avg = {:.2f}'.format(id_, total, average))