我有一个如下所示的数据框：

Name Variable Field

A 2.3 412

A 2.9 861

A 3.5 1703

B 3.5 1731

A 4.0 2609

B 4.0 2539

A 4.6 2821

B 4.6 2779

A 5.2 3048

B 5.2 2979

A 5.8 3368

B 5.8 3216

如您所见，我有“变量”列的重复值。我想为A和B之间的每个变量计算delta（％）。我想生成的数据帧是：

Name Variable Field Ref field (A) Delta (A - B)

A 2.3 412 412 0.0%

A 2.9 861 861 0.0%

A 3.5 1703 1703 0.0%

B 3.5 1731 1703 -1.6%

A 4.0 2609 2609 0.0%

B 4.0 2539 2609 2.8%

A 4.6 2821 2821 0.0%

B 4.6 2779 2821 1.5%

A 5.2 3048 3048 0.0%

B 5.2 2979 3048 2.3%

A 5.8 3368 3368 0.0%

B 5.8 3216 3368 4.7%

我已经过一些东西，比如：

df["Ref field (A)"] = df.apply(lambda row:df[(df["Variable"] == row["Variable"]) & (df["Name"] == "A")]["Field"][0],axis=1)

但它只是不起作用......：

File "pandas/_libs/index.pyx", line 106, in pandas._libs.index.IndexEngine.get_value

File "pandas/_libs/index.pyx", line 114, in pandas._libs.index.IndexEngine.get_value

File "pandas/_libs/index.pyx", line 162, in pandas._libs.index.IndexEngine.get_loc

File "pandas/_libs/hashtable_class_helper.pxi", line 958, in pandas._libs.hashtable.Int64HashTable.get_item

File "pandas/_libs/hashtable_class_helper.pxi", line 964, in pandas._libs.hashtable.Int64HashTable.get_item

KeyError: (0, u'occurred at index 0')

解决办法：A'每个'Variable'组只有一个值，创建一个Series并映射值以获取引用。

s = df[df.Name.eq('A')].set_index('Variable').Field

df['RefA'] = df.Variable.map(s)

df['Delta'] = (df.RefA - df.Field)/df.Field*100