pandas :内部联接不返回任何行 [英] Pandas: Inner Join returns no rows

问题描述

DataFrame 1(commits)

DataFrame 1 (commits)

CommitID  | COMMITTER  
------------------------
  1       | A         
  2       | B         
  3       | B         

DataFrame 2(files)

DataFrame 2 (files)

CommitID  | MOD
------------------------
  1       | 0         
  2       | 1         
  3       | 7       

我试图用df.merge内部连接这些DataFrame:

I tried to inner join these DataFrames with df.merge:

files.merge(right=commits, how='inner',left_on="CommitID", right_on="CommitID")

但是，尽管列名相同，但它不返回任何行.

But it doesn't return any rows, although the column name is identical.

推荐答案

CommitID列存在与dtypes不同的问题.

There is problem different dtypes of column CommitID.

需要通过以下方式检查它们:

Need check them by:

print (files['CommitID'].dtypes)
print (commits['CommitID'].dtypes)

然后通过astype转换为相同的内容:

And then convert by astype to same:

#change only object
files['CommitID'] = files['CommitID'].astype(int)
commits['CommitID'] = commits['CommitID'].astype(int)

---

#change only int
files['CommitID'] = files['CommitID'].astype(str)
commits['CommitID'] = commits['CommitID'].astype(str)

您的代码可以简化-省略默认how='inner并仅使用on:

Yur code can be simplify - omit default how='inner and use only on:

df = files.merge(right=commits, on="CommitID")
print (df)
   CommitID  MOD COMMITTER
0         1    0         A
1         2    1         B
2         3    7         B

或者如果两个DataFrames中只有相同的联接列:

Or if only same joined columns in both DataFrames:

df = files.merge(right=commits)
print (df)
   CommitID  MOD COMMITTER
0         1    0         A
1         2    1         B
2         3    7         B

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