从 pandas 数据框中匹配和提取值 [英] Matching and extracting values from pandas dataframe

问题描述

我正在尝试在熊猫数据框中找到匹配的值.找到匹配项后，我要对数据框的行执行一些操作.

I'm trying to find matching values in a pandas dataframe. Once a match is found I want to perform some operations on the row of the dataframe.

当前我正在使用此代码:

Currently I'm using this Code:

import pandas as pd

d = {'child_id': [1,2,5,4,7,8,9,10],
 'parent_id': [3,4,1,3,11,6,12,13],
 'content': ["thon","pan","py","das","ten","sor","js","on"]}

df = pd.DataFrame(data=d)

df2 = pd.DataFrame(columns = ("content_child", "content_parent"))

for i in range(len(df)):

        for j in range(len(df)):

            if str(df['child_id'][j]) == str(df['parent_id'][i]):
                content_child = str(df["content"][i])

                content_parent = str(df["content"][j])

                s = pd.Series([content_child, content_parent], index=['content_child', 'content_parent'])
                df2 = df2.append(s, ignore_index=True)
            else:
                pass

 print(df2)

这将返回:

  content_child content_parent
0           pan            das
1            py           thon

我尝试使用df.loc函数，但仅成功从子级获取内容或从父级获取内容

I tried using df.loc functions, but I only succeed in getting either Content from child or Content from parent:

df.loc[df.parent_id.isin(df.child_id),['child_id','content']]

返回:

      child_id content
1         2     pan
2         5      py

除了我编写的循环以外，还有其他快速的选择吗?

Is there an fast alternative to the loop I have written?

推荐答案

如果左侧部分child_id等于右侧部分parent_id，则可以仅使用join数据帧作为条件.

You can use just join data frames with condition if left part child_id is equal to right part parent_id.

df.set_index('parent_id').join(df.set_index('child_id'), rsuffix='_').dropna()

此代码将创建两个ID为parent_id和child_id的数据表.然后像往常一样将它们加入SQL连接.毕竟，删除NaN值并获得content列.您要哪一个.有2个内容列.其中之一是父内容，第二是子内容.

this code will create two data tables with ids parent_id and child_id. Then join them as usual SQL join. After all drop NaN values and get content column. Which is what you want. There are 2 content columns. one of them is parent content and second is child content.

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