使用相同的列，不同的索引级别对DataFrame进行算术和对齐

Question

我有两个熊猫DataFrames-weight在Land Use列上有一个简单的Index 。concentration在Land Use和上具有MultiIndex Parameter。

import pandas
from io import StringIO

conc_string = StringIO("""\
Land Use,Parameter,1E,1N,1S,2
Airfield,BOD5 (mg/l),0.418,0.118,0.226,1.063
Airfield,Ortho P (mg/l),0.002,0.001,0.001,0.002
Airfield,TSS (mg/l),1.773,11.47,0.862,0.183
Airfield,Zn (mg/l),0.001,0.001,4.95E-05,0.001
"Commercial",BOD5 (mg/l),0.036,0.0419,,0.315
"Commercial",Cu (mg/l),4.37E-05,7.34E-05,,0.00039
"Commercial",O&G (mg/l),0.0385,0.127,,0.263
Open Space,TSS (mg/l),0.371,3.01,1.209,0.147
Open Space,Zn (mg/l),0.0127,0.0069,0.0132,0.007
"Parking Lot",BOD5 (mg/l),0.924,0.0668,2.603,3.19
"Parking Lot",O&G (mg/l),1.02,0.149,1.347,1.88
"Rooftops",BOD5 (mg/l),0.135,1.00,0.0562,0.310""")

weight_string = StringIO("""\
Land Use,1E,1N,1S,2
Airfield,0.511,0.0227,0.0616,0.394
Commercial,0.0005,0.1704,0,0.1065
Open Space,0.0008,0.005,0.0002,0.0004
"Parking Lot",0.33,0.514,0.252,0.171
Rooftops,0.081,0.028,8.50E-05,0.003""")

concentration = pandas.read_csv(conc_string, index_col=[0,1])
weight = pandas.read_csv(weight_string, index_col=0)

在这种情况下，列（1E，1N，1S和2）是流域盆地。

我想做的是将所有浓度除以Parameter盆地（列名）和的权重Land Use。

我在这里运气不好。concentration / weight当然是行不通的。我没有很多运气堆叠数据帧并加入

wstk = pandas.DataFrame(weight.stack())
wstk.index.names = ['Land Use', 'Basin']
wstk.rename(columns={0:'weight'}, inplace=True)

cstk = pandas.DataFrame(concentration.stack())
cstk.index.names = ['Land Use', 'Parameter', 'Basin']
cstk.rename(columns={0:'concentration'}, inplace=True)

wstk.join(cstk, on=['Land Use', 'Basin']) # fails 
cstk.join(wstk, on=['Land Use', 'Basin']) # fails

当我离开onkwarg时，最后两行不会引发错误，但是会返回NaNjoined列的结果。如果我在两个堆叠的DataFrame上都放下索引，它们也会失败（例如，wstk.reset_index(inplace=True)在连接之前执行）。

有什么建议？

Answer 1

使用DataFramediv方法并为您要广播的多索引传递matchkey：

从文档中div：

level : int or name
    Broadcast across a level, matching Index values on the
    passed MultiIndex level

In [39]: concentration.div(weight, level='Land Use')
Out[39]:
                                    1E          1N           1S           2
Land Use    Parameter
Airfield    BOD5 (mg/l)       0.818004    5.198238     3.668831    2.697970
            Ortho P (mg/l)    0.003914    0.044053     0.016234    0.005076
            TSS (mg/l)        3.469667  505.286344    13.993506    0.464467
            Zn (mg/l)         0.001957    0.044053     0.000804    0.002538
Commercial  BOD5 (mg/l)      72.000000    0.245892          NaN    2.957746
            Cu (mg/l)         0.087400    0.000431          NaN    0.003662
            O&G (mg/l)       77.000000    0.745305          NaN    2.469484
Open Space  TSS (mg/l)      463.750000  602.000000  6045.000000  367.500000
            Zn (mg/l)        15.875000    1.380000    66.000000   17.500000
Parking Lot BOD5 (mg/l)       2.800000    0.129961    10.329365   18.654971
            O&G (mg/l)        3.090909    0.289883     5.345238   10.994152
Rooftops    BOD5 (mg/l)       1.666667   35.714286   661.176471  103.333333