如何根据列值从数据帧中选择行？

Question

sql prettyprint-override">SELECT *
FROM table
WHERE colume_name = some_value

我试图查看熊猫的文档，但我没有立即找到答案。

Answer 1

若要选择列值等于标量some_value的行，请使用==:

df.loc[df['column_name'] == some_value]

若要选择列值在可迭代some_values中的行，请使用isin:

df.loc[df['column_name'].isin(some_values)]

使用&组合多个条件：

df.loc[(df['column_name'] >= A) & (df['column_name'] <= B)]

df['column_name'] >= A & df['column_name'] <= B

df['column_name'] >= (A & df['column_name']) <= B

df.loc[df['column_name'] != some_value]

df.loc[~df['column_name'].isin(some_values)]

例如,

import pandas as pd
import numpy as np
df = pd.DataFrame({'A': 'foo bar foo bar foo bar foo foo'.split(),
                   'B': 'one one two three two two one three'.split(),
                   'C': np.arange(8), 'D': np.arange(8) * 2})
print(df)
#      A      B  C   D
# 0  foo    one  0   0
# 1  bar    one  1   2
# 2  foo    two  2   4
# 3  bar  three  3   6
# 4  foo    two  4   8
# 5  bar    two  5  10
# 6  foo    one  6  12
# 7  foo  three  7  14

print(df.loc[df['A'] == 'foo'])

收益率

     A      B  C   D
0  foo    one  0   0
2  foo    two  2   4
4  foo    two  4   8
6  foo    one  6  12
7  foo  three  7  14

如果您有多个要包含的值，请将它们放入列表中（或者更一般地，任何可迭代的值），并使用isin:

print(df.loc[df['B'].isin(['one','three'])])

     A      B  C   D
0  foo    one  0   0
1  bar    one  1   2
3  bar  three  3   6
6  foo    one  6  12
7  foo  three  7  14

df = df.set_index(['B'])
print(df.loc['one'])

       A  C   D
B              
one  foo  0   0
one  bar  1   2
one  foo  6  12

df.loc[df.index.isin(['one','two'])]

       A  C   D
B              
one  foo  0   0
one  bar  1   2
two  foo  2   4
two  foo  4   8
two  bar  5  10
one  foo  6  12