python - 计算字典 pandas 列中的项目

Question

我有一个数据框，其中有一列包含字典。我想计算整个列中字典键的出现次数。

一种方法如下:

import pandas as pd
from collections import Counter

df = pd.DataFrame({"data": [{"weight": 3, "color": "blue"},
{"size": 5, "weight": 2},{"size": 3, "color": "red"}]})

c = Counter()

for index, row in df.iterrows():
  for item in list(row["data"].keys()):
    c[item] += 1

print(c)

哪个给

Counter({'weight': 2, 'color': 2, 'size': 2})

有没有更快的方法？

Answer 1

一种更快的方法是用 itertools.chain 展平该列并根据结果构建一个 Counter(它将只包含字典键):

from itertools import chain

Counter(chain.from_iterable(df.data.values.tolist()))
# Counter({'weight': 2, 'color': 2, 'size': 2})

---

时间:

def OP(df):
    c = Counter()
    for index, row in df.iterrows():
        for item in list(row["data"].keys()):
            c[item] += 1

%timeit OP(df)
# 570 µs ± 49.4 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)

%timeit Counter(chain.from_iterable(df.data.values.tolist()))
# 14.2 µs ± 902 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)