pandas python 如何计算数据帧中的记录数或行数 [英] pandas python how to count the number of records or rows in a dataframe

问题描述

显然是 Pandas 的新手.我如何简单地计算数据框中的记录数.

Obviously new to Pandas. How can i simply count the number of records in a dataframe.

我本以为这么简单的事情就可以做到，但我似乎无法在搜索中找到答案……可能是因为它太简单了.

I would have thought some thing as simple as this would do it and i can't seem to even find the answer in searches...probably because it is too simple.

cnt = df.count
print cnt

上面的代码实际上只是打印了整个 df

the above code actually just prints the whole df

推荐答案

关于您的问题...计数一个字段?我决定把它作为一个问题，但我希望它有所帮助...

Regards to your question... counting one Field? I decided to make it a question, but I hope it helps...

假设我有以下 DataFrame

Say I have the following DataFrame

import numpy as np
import pandas as pd

df = pd.DataFrame(np.random.normal(0, 1, (5, 2)), columns=["A", "B"])

您可以按以下方式计算一列

You could count a single column by

df.A.count()
#or
df['A'].count()

两者都评估为 5.

很酷的事情(或许多 w.r.t. pandas 之一)是，如果您有 NA 值，count 会考虑这一点.

The cool thing (or one of many w.r.t. pandas) is that if you have NA values, count takes that into consideration.

如果我这样做了

df['A'][1::2] = np.NAN
df.count()

结果是

 A    3
 B    5

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