使用rpy2调用R的dea()时，如何处理RTYPES.NILSXP返回值？

在Python中使用rpy2调用R语言Benchmarking包的dea()函数时，部分返回值（如dual、primal等）会呈现RTYPES.NILSXP类型，无法像eff、lambda那样直接获取ndarray或int格式的数据。

环境配置代码 #

# imports 
import pandas as pd

import rpy2
import rpy2.robjects as robjects
import rpy2.robjects.packages as rpackages
from rpy2.robjects.vectors import StrVector
from rpy2.robjects.packages import importr
utils = rpackages.importr('utils')
utils.chooseCRANmirror(ind=1)

# helps work with pd.DataFrame objects
from rpy2.robjects import pandas2ri

from rpy2.robjects.conversion import localconverter

# import the R library into Python
packnames = ('Benchmarking')
utils.install_packages(StrVector(packnames))

Benchmarking = importr('Benchmarking')
base = importr('base')

data = pd.read_csv("path/to_data.csv")

# call the function I want and store it in a variable
with localconverter(robjects.default_converter + pandas2ri.converter):
  crs = Benchmarking.dea(data['Age'], data['CO2'], RTS='crs', ORIENTATION='in')

错误现象 #

调用dea()后，crs['eff']或crs['lambda']可正常返回ndarray：

crs
# 输出：
# {'eff': [1.    0.625 0.5  ], 'lambda': [[1.   0.   0.  ]
#  [1.25 0.   0.  ]
#  [1.5  0.   0.  ]], 'objval': [1.    0.625 0.5  ], 'RTS': [1] "crs"
# , 'primal': <rpy2.rinterface_lib.sexp.NULLType object at 0x00000220BCB0D1C0> [RTYPES.NILSXP], 'dual': <rpy2.rinterface_lib.sexp.NULLType object at 0x00000220BCB0D1C0> [RTYPES.NILSXP], 'ux': <rpy2.rinterface_lib.sexp.NULLType object at 0x00000220BCB0D1C0> [RTYPES.NILSXP], 'vy': <rpy2.rinterface_lib.sexp.NULLType object at 0x00000220BCB0D1C0> [RTYPES.NILSXP], 'gamma': function (x)  .Primitive("gamma")
# , 'ORIENTATION': [1] "in"
# , 'TRANSPOSE': [1] FALSE
# , 'param': <rpy2.rinterface_lib.sexp.NULLType object at 0x00000220BCB0D1C0> [RTYPES.NILSXP], }

但提取crs['dual']等返回值时，仅得到NULL对象：

crs['dual']
# 输出：
# <rpy2.rinterface_lib.sexp.NULLType object at 0x00000220BCB0D1C0> [RTYPES.NILSXP]

错误尝试及报错 #

尝试用fetch()方法加载该对象时，报错：

rpy2.robjects.packages.PackageData.fetch(crs['dual'])
# 报错：
# TypeError: PackageData.fetch() missing 1 required positional argument: 'name'

传入名称参数后仍报错：

rpy2.robjects.packages.PackageData.fetch(r_from_df_crs['dual'], 'dual')
# 报错：
# AttributeError: 'NULLType' object has no attribute '_datasets'

尝试用rpackages.data()转换对象也报错：

my_crs = rpackages.data(crs)
# 报错：
# AttributeError: 'OrdDict' object has no attribute '__rdata__'

解决方案 #

问题根源是调用dea()函数时未传入SLACK=True和DUAL=True参数，导致dual、primal等相关结果默认返回NULL值。修改后的调用代码如下：

with localconverter(robjects.default_converter + pandas2ri.converter):
  crs = Benchmarking.dea(data['Age'], data['CO2'], RTS='crs', ORIENTATION='in', SLACK=True, DUAL=True)

添加这两个参数后，dual、primal等返回值会正常生成，可像eff、lambda一样转换为Python可直接使用的数据格式。

内容的提问来源于stack exchange，提问作者Sully H