[英]Add values to one column of a pandas dataframe based on the values in another
[英]Add rows from one dataframe to another based on missing values in a given column pandas
我一直在寻找答案,但找不到它。 我有两个数据框,一个是target
,另一个backup
都具有相同的列。 我想要做的是查看给定的列并将所有行从backup
添加到target
,这些行不在target
中。 最直接的解决方案是:
import pandas as pd
import numpy as np
target = pd.DataFrame({
"key1": ["K1", "K2", "K3", "K5"],
"A": ["A1", "A2", "A3", np.nan],
"B": ["B1", "B2", "B3", "B5"],
})
backup = pd.DataFrame({
"key1": ["K1", "K2", "K3", "K4", "K5"],
"A": ["A1", "A", "A3", "A4", "A5"],
"B": ["B1", "B2", "B3", "B4", "B5"],
})
merged = target.copy()
for item in backup.key1.unique():
if item not in target.key1.unique():
merged = pd.concat([merged, backup.loc[backup.key1 == item]])
merged.reset_index(drop=True, inplace=True)
给予
key1 A B
0 K1 A1 B1
1 K2 A2 B2
2 K3 A3 B3
3 K5 NaN B5
4 K4 A4 B4
现在我只使用 pandas 尝试了几件事,但它们都不起作用。
# Does not work because it creates duplicate lines and if dropped, the updated rows which are different will not be dropped -- compare the line with A or NaN
pd.concat([target, backup]).drop_duplicates()
key1 A B
0 K1 A1 B1
1 K2 A2 B2
2 K3 A3 B3
3 K5 NaN B5
1 K2 A B2
3 K4 A4 B4
4 K5 A5 B5
# Does not work because the backup would overwrite data in the target -- NaN
pd.merge(target, backup, how="right")
key1 A B
0 K1 A1 B1
1 K2 A B2
2 K3 A3 B3
3 K4 A4 B4
4 K5 A5 B5
重要的是,它不是这篇文章的副本,因为我不想有一个新列,更重要的是, target
中的值不是NaN
,它们根本不存在。 此外,如果那时我将使用建议的合并列, target
中的NaN
将被backup
中不需要的值替换。
它不是使用combine_first pandas 的这篇文章的副本,因为在这种情况下, NaN
由来自backup
的值填充,这是错误的:
target.combine_first(backup)
key1 A B
0 K1 A1 B1
1 K2 A2 B2
2 K3 A3 B3
3 K5 A4 B5
4 K5 A5 B5
target.join(backup, on=["key1"])
让我很烦
ValueError: You are trying to merge on object and int64 columns. If you wish to proceed you should use pd.concat
我真的没有得到,因为它们都是纯字符串,并且建议的解决方案不起作用。
所以我想问一下,我错过了什么? 如何使用一些pandas
方法来做到这一点? 非常感谢。
在boolean indexing
中使用由target.key1
过滤的Series.isin
中不存在的过滤backup
行的concat
:
merged = pd.concat([target, backup[~backup.key1.isin(target.key1)]])
print (merged)
key1 A B
0 K1 A1 B1
1 K2 A2 B2
2 K3 A3 B3
3 K5 NaN B5
3 K4 A4 B4
也许您可以在df.drop_duplicates()
中使用“子集”参数来试试这个?
pd.concat([target, backup]).drop_duplicates(subset = "key1")
这给出了 output:
key1 A B
0 K1 A1 B1
1 K2 A2 B2
2 K3 A3 B3
3 K5 NaN B5
3 K4 A4 B4
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