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[英]How can I subset a data frame based on a list of unique values in a columns of that same data frame?
[英]How can I subset a data frame for unique rows using repeating values from a column in another data frame in python?
我有 2 个数据框。 我想根据 df_2 对 df_1 进行子集化,以便结果数据框中的行对应于 df_2 中的行。 以下是两个示例数据框:
df_1 = pd.DataFrame({
"ID": ["Lemon","Banana","Apple","Cherry","Tomato","Blueberry","Avocado","Lime"],
"Color": ["Yellow","Yellow","Red","Red","Red","Blue","Green","Green"]})
df_2 = pd.DataFrame({"Color": ["Red","Blue","Yellow","Green","Red","Yellow"]})
我想要的输出是 df_3,其中“颜色”列与 df_2 中的相同:
df_3 = pd.DataFrame({
"ID": ["Apple","Blueberry","Lemon","Avocado","Cherry","Banana"],
"Color": ["Red","Blue","Yellow","Green","Red","Yellow"]})
当我合并 df_1 和 df_2 时,我得到重复的行,因为 df_2 中的大多数行在 df_1 中有多个匹配项。
merged = df_2.merge(df_1, how="left", on="Color")
删除重复项适用于“黄色”颜色,因为它在 df_2 中的值和 df_1 中的选项的比率为 2:2,但对于“红色”或“绿色”则不能正常工作,因为它们的比率为 2:3和 1:2 的比例,导致额外的行。
no_duplicates = merged.drop_duplicates(subset = "ID")
有没有办法对 df_1 进行子集化,其中 df_2 中第一次出现“Red”会提取 df_1 中第一次出现的“Red”,df_2 中第二次出现的“Red”会提取 df_1 中第二次出现的“Red”,等等。? 除非别无选择,否则我宁愿不使用循环。 谢谢你。
尝试添加的指标列都df_1
和df_2
与groupby cumcount
获得位置,以及:
df_1['i'] = df_1.groupby('Color').cumcount()
df_2['i'] = df_2.groupby('Color').cumcount()
df_1
:
ID Color i
0 Lemon Yellow 0
1 Banana Yellow 1
2 Apple Red 0
3 Cherry Red 1
4 Tomato Red 2
5 Blueberry Blue 0
6 Avocado Green 0
7 Lime Green 1
df_2
:
Color i
0 Red 0
1 Blue 0
2 Yellow 0
3 Green 0
4 Red 1
5 Yellow 1
merged_df = df_1.merge(df_2, how='right', on=['Color', 'i']).drop('i', axis=1)
merged_df
:
ID Color
0 Apple Red
1 Blueberry Blue
2 Lemon Yellow
3 Avocado Green
4 Cherry Red
5 Banana Yellow
或者 create pass 系列直接merge
(这使df_1
和df_2
不受影响):
merged_df = df_1.merge(
df_2, how='right',
left_on=['Color', df_1.groupby('Color').cumcount()],
right_on=['Color', df_2.groupby('Color').cumcount()]
).drop('key_1', axis=1)
merged_df
:
ID Color
0 Apple Red
1 Blueberry Blue
2 Lemon Yellow
3 Avocado Green
4 Cherry Red
5 Banana Yellow
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