pandas之dataframe去掉冗余行以及左链接合并dataframe

去掉冗余行

重现冗余数据

zylMBP:~ zhangyalin$ python3
Python 3.6.5 (v3.6.5:f59c0932b4, Mar 28 2018, 03:03:55) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import pandas as pd
>>> df = pd.DataFrame({"A":["foo", "foo", "foo", "bar"]})
>>> print(df)
     A
0  foo
1  foo
2  foo
3  bar

三种方式去冗余数据

方式1

>>> df.drop_duplicates(subset=['A'], keep=False)
     A
3  bar
>>>

keep=False表示删除全部冗余行。

方式2

>>> df.drop_duplicates(subset=['A'], keep='first')
     A
0  foo
3  bar
>>>

keep=='first'表示保留第一行数据，其余冗余行删除。

方式3

>>> df.drop_duplicates(subset=['A'], keep='last')
     A
2  foo
3  bar
>>>

keep=='last'表示保留最后一行数据，其余冗余行删除。

pandas左链接两个dataframe

result = pd.merge(left, right, how='left', on=['key1', 'key2'])

参考

pandas.DataFrame.drop_duplicates Merge, join, and concatenate