pandas 如何替换熊猫数据框中的列的选定行的值？
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how to replace values of selected row of a column in panda's dataframe?
提问by Bilal Butt
i have train dataset which has 12 columns.
我有 12 列的训练数据集。
I want to select Cabincolumn rows according to Pclasscolumn's value 1. And then replace value of selected rows of Cabin column with 1.
我想根据Pclass列的值 1选择Cabin列行。然后将 Cabin 列的选定行的值替换为 1。
i did following code but it replace all values of cabin column with 1 even NaN values replace by 1.How i can replace only selected rows?
我做了下面的代码，但它用 1 替换了小屋列的所有值，甚至将 NaN 值替换为 1。如何只替换选定的行？
train['Cabin'] =train[train['Pclass']==1]['Cabin']=1
回答by jezrael
You can select by locwith condition rows of column Cabinand set to scalar:
您可以loc根据列的条件行进行选择Cabin并设置为标量：
train.loc[train['Pclass'] == 1, 'Cabin'] = 1
And your code replace all values to 1because is is same as:
并且您的代码将所有值替换为1因为与以下内容相同：
train['Cabin'] = 1
Sample:
样品：
train = pd.DataFrame({'Pclass':[1,2,3,1,2],
'Cabin':[10,20,30,40,50]})
print (train)
Cabin Pclass
0 10 1
1 20 2
2 30 3
3 40 1
4 50 2
train.loc[train['Pclass'] == 1, 'Cabin'] = 1
print (train)
Cabin Pclass
0 1 1
1 20 2
2 30 3
3 1 1
4 50 2
