基于价值的 pandas 查询 [英] Pandas lookup based on value

问题描述

我有以下DataFrame:

I have the following DataFrame:

Date    best    a    b    c    d
1990    a       5    4    7    2
1991    c       10   1    2    0
1992    d       2    1    4    12
1993    a       5    8    11   6

我想制作一个数据框，如下所示:

I would like to make a dataframe as follows:

Date    best    value   
1990    a       5
1991    c       2
1992    d       12
1993    a       5

所以我正在寻找使用列名基于另一个行值的值.例如，第二个df中1990年的值应从第一个df中查找"a"，第二行应从第一个df中查找"c"(= 2).

So I am looking to find a value based on another row value by using column names. For instance, the value for 1990 in the second df should lookup "a" from the first df and the second row should lookup "c" (=2) from the first df.

有什么想法吗?

推荐答案

有一个内置的

There is a built in lookup function that can handle this type of situation (looks up by row/column). I don't know how optimized it is, but may be faster than the apply solution.

In [9]: df['value'] = df.lookup(df.index, df['best'])

In [10]: df
Out[10]: 
   Date best   a  b   c   d  value
0  1990    a   5  4   7   2      5
1  1991    c  10  1   2   0      2
2  1992    d   2  1   4  12     12
3  1993    a   5  8  11   6      5

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