有没有更有效的方法来对应不同表中的值？

Question

我可以更高效地运行此代码吗？这是一个简化的示例，实际上我正在使用一个包含近一百万个条目的表并执行多个循环。运行需要很长时间。欢迎任何建议！

import pandas as pd

codeTable = {'Code': [1,2,3], 'Activity': ['a1', 'a2', 'a3']}
Table = {'Code':[1,2,4,3,6,7,15,2,3,4]}

df1 = pd.DataFrame(data = codeTable)
df2 = pd.DataFrame(data = Table)
df2['Activity'] = "-"
for i in range (0,df2.shape[0]):
    if df2['Code'][i] in set(df1['Code']):
        df2['Activity'][i] = df1['Activity'][ df1['Activity'][df1['Code'] == df2['Code'][i] ].index [0] ]
    else:
        df2['Activity'][i] = "-"