英文:
Conditional merging of two dataframes in python3.7
问题
以下是您要翻译的内容：
我有以下的数据框
col1 term1 term2
ab|a ab a
cd cd
我想要将这个数据框与另一个数据框（df2）合并，使用“term1”和“term2”两列，但在值为None时跳过/忽略（就像在第2行中一样）。我试图在一个for循环中使用if/else条件来实现这一目标。请查看下面的伪代码（这不是一个功能性代码，因为它也显示错误）。
这是正确的方法吗，还有更好的方法吗？
df1 = pd.concat([df["col1"], df["col1"].str.split("|", expand=True)], axis=1)
df1.rename(columns={0: 'term1', 1: 'term2'}, inplace=True)
for index, row in df1.iterrows():
if row['term1'] is None:
break
else:
row = row.to_frame()
print(row)
row.merge(df2, how='inner', left_on='term1', right_on='STR')
<details>
<summary>英文:</summary>
I have following dataframe
col1 term1 term2
ab|a ab a
cd cd
I would like to merge this dataframe to another dataframe (df2) using both the columns "term1" and "term2" but skip/ignore when it is None (like in row 2). I am trying to use if/else condition here in a for loop. Please see the pseudocode below (this is not a functional code as it is showing error as well).
Is it a right approach or there is nicer way to do this.
df1 = pd.concat([df["col1
"],df["col1"].str.split("|", expand=True)], axis=1)
df1.rename(columns={0: 'term1', 1: 'term2'}, inplace=True)
for index, row in df1.iterrows():
if row['term1'] is None:
break
else:
row = row.to_frame()
print (row)
row.merge(df2, how = 'inner', left_on = 'term1', right_on = 'STR')
</details>
# 答案1
**得分**: 1
在 pandas 数据框中使用循环是一种代码异味。为了排除具有空值的行，在合并之前，只需删除它们。您可以首先使用 pandas 的 dropna ([文档][1])。类似这样：
```python
df1 = df1.dropna(subset=["term1", "term2"])
然后应用 pandas 的 merge (文档)：
df = df1.merge(df2, on=["term1", "term2"])
为了使代码更简短，您可以首先定义 merge_columns = ["term1", "term2"] 以在 dropna 和 merge 方法中使用。您还可以在合并中直接进行筛选，我只是分步进行以便清晰明了。
希望对您有所帮助。
英文:
A loop in pandas dataframes is a code smell. In order to exclude rows with null values, just drop them before merging. You could first use pandas' dropna (doc). Something like this:
df1 = df1.dropna(subset=["term1", "term2"])
And then apply pandas' merge (doc):
df = df1.merge(df2, on=["term1", "term2"])
In order to make the code shorter, you could first define merge_columns = ["term1", "term2"] to be used in the dropna and merge method. You could also make the filter right inside the merge, I just did it step by step to be clear.
Hope it helps.
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