pandas concat ignore_index 不起作用 [英] pandas concat ignore_index doesn't work
问题描述
我正在尝试对数据框进行列绑定,但在使用 Pandas concat
时遇到问题,因为 ignore_index=True
似乎不起作用:
I am trying to column-bind dataframes and having issue with pandas concat
, as ignore_index=True
doesn't seem to work:
df1 = pd.DataFrame({'A': ['A0', 'A1', 'A2', 'A3'],
'B': ['B0', 'B1', 'B2', 'B3'],
'D': ['D0', 'D1', 'D2', 'D3']},
index=[0, 2, 3,4])
df2 = pd.DataFrame({'A1': ['A4', 'A5', 'A6', 'A7'],
'C': ['C4', 'C5', 'C6', 'C7'],
'D2': ['D4', 'D5', 'D6', 'D7']},
index=[ 5, 6, 7,3])
df1
# A B D
# 0 A0 B0 D0
# 2 A1 B1 D1
# 3 A2 B2 D2
# 4 A3 B3 D3
df2
# A1 C D2
# 5 A4 C4 D4
# 6 A5 C5 D5
# 7 A6 C6 D6
# 3 A7 C7 D7
dfs = [df1,df2]
df = pd.concat( dfs,axis=1,ignore_index=True)
print df
结果是
0 1 2 3 4 5
0 A0 B0 D0 NaN NaN NaN
2 A1 B1 D1 NaN NaN NaN
3 A2 B2 D2 A7 C7 D7
4 A3 B3 D3 NaN NaN NaN
5 NaN NaN NaN A4 C4 D4
6 NaN NaN NaN A5 C5 D5
7 NaN NaN NaN A6 C6 D6
即使我使用
df1.reset_index()
df2.reset_index()
然后尝试
pd.concat([df1,df2],axis=1)
它仍然产生相同的结果!
it still produces the same result!
推荐答案
如果我理解正确,这就是您想要做的.
If I understood you correctly, this is what you would like to do.
import pandas as pd
df1 = pd.DataFrame({'A': ['A0', 'A1', 'A2', 'A3'],
'B': ['B0', 'B1', 'B2', 'B3'],
'D': ['D0', 'D1', 'D2', 'D3']},
index=[0, 2, 3,4])
df2 = pd.DataFrame({'A1': ['A4', 'A5', 'A6', 'A7'],
'C': ['C4', 'C5', 'C6', 'C7'],
'D2': ['D4', 'D5', 'D6', 'D7']},
index=[ 4, 5, 6 ,7])
df1.reset_index(drop=True, inplace=True)
df2.reset_index(drop=True, inplace=True)
df = pd.concat( [df1, df2], axis=1)
给出:
A B D A1 C D2
0 A0 B0 D0 A4 C4 D4
1 A1 B1 D1 A5 C5 D5
2 A2 B2 D2 A6 C6 D6
3 A3 B3 D3 A7 C7 D7
实际上,我本来希望 df = pd.concat(dfs,axis=1,ignore_index=True)
给出相同的结果.
Actually, I would have expected that df = pd.concat(dfs,axis=1,ignore_index=True)
gives the same result.
这是 jreback 的精彩解释:
ignore_index=True
‘ignores’,意思是没有在连接轴上对齐.它只是按照传递的顺序将它们粘贴在一起,然后为实际索引重新分配一个范围(例如 range(len(index))
)所以加入非重叠索引(假设在示例中为 axis=1
)的区别在于,使用 ignore_index=False
(默认值),您会得到索引,并使用 ignore_index=True
你得到一个范围.
ignore_index=True
‘ignores’, meaning doesn’t align on the joining axis. it simply pastes them together in the order that they are passed, then reassigns a range for the actual index (e.g.range(len(index))
) so the difference between joining on non-overlapping indexes (assumeaxis=1
in the example), is that withignore_index=False
(the default), you get the concat of the indexes, and withignore_index=True
you get a range.
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