Question

我想将数据框中列的第一个n元素替换为我保存的另一个pd.series。举个例子，

        category   price    store  testscore
0       Cleaning   11.42  Walmart        NaN
1       Cleaning   23.50      Dia        NaN
2  Entertainment   19.99  Walmart        NaN
3  Entertainment   15.95     Fnac        NaN
4           Tech   55.75      Dia        NaN
5           Tech  111.55  Walmart        NaN

在这里，我想用一组新的字符串替换testscore中的前三个NaN。

想象一下，我有一个变量：

cats = pd.Series(df['category'][0:2])

我可以将它放在testscore列中......

        category   price    store      testscore
0       Cleaning   11.42  Walmart       Cleaning
1       Cleaning   23.50      Dia       Cleaning
2  Entertainment   19.99  Walmart  Entertainment
3  Entertainment   15.95     Fnac            NaN
4           Tech   55.75      Dia            NaN
5           Tech  111.55  Walmart            NaN

但每当我尝试这样做时，它都不会工作。

创建此假数据集的代码：

import pandas as pd
import numpy as np

df = pd.DataFrame({'category': ['Cleaning', 'Cleaning', 'Entertainment', 'Entertainment', 'Tech', 'Tech'],
                        'store': ['Walmart', 'Dia', 'Walmart', 'Fnac', 'Dia','Walmart'],
                        'price':[11.42, 23.50, 19.99, 15.95, 55.75, 111.55],
                        'testscore': [np.nan, np.nan, np.nan, np.nan, np.nan, np.nan]})

print(df)

df2 = pd.DataFrame({'category': ['Cleaning', 'Cleaning', 'Entertainment', 'Entertainment', 'Tech', 'Tech'],
                        'store': ['Walmart', 'Dia', 'Walmart', 'Fnac', 'Dia','Walmart'],
                        'price':[11.42, 23.50, 19.99, 15.95, 55.75, 111.55],
                        'testscore': ['Cleaning', 'Cleaning', 'Entertainment', np.nan, np.nan, np.nan]})

print(df2)

Answer 1

只需使用df.loc：

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你得到：

import pandas as pd
import numpy as np

df = pd.DataFrame({'category': ['Cleaning', 'Cleaning', 'Entertainment', 'Entertainment', 'Tech', 'Tech'],
                        'store': ['Walmart', 'Dia', 'Walmart', 'Fnac', 'Dia','Walmart'],
                        'price':[11.42, 23.50, 19.99, 15.95, 55.75, 111.55],
                        'testscore': [np.nan, np.nan, np.nan, np.nan, np.nan, np.nan]})


cats = pd.Series(df['category'][:3]) # 3 elements

df.loc[:3,'testscore'] = cats # Assign first 3

print(df)

Answer 2

将find . ... -path ./logs ...与参数fillna：

一起使用

limit

输出：

df['testscore'] = df.testscore.fillna(df.category, limit=3)
df

替换pandas dataframe列中的前n个元素

2 个答案: