Trying to access R class methods and fields within Python using rpy2 - r

Question

I am using rpy2 to import a library from CRAN repository called "MatrixEQTL" to run in within Python using importr, here is my attempt:
import rpy2.robjects as robjects
from rpy2.robjects.packages import importr
robjects.r('install.packages("MatrixEQTL")')
mtrql = importr('MatrixEQTL')
I am trying to access both class fields as well as class methods but I failed here is what the class looks like when printing into the python shell:
# to view class SlicedData of MatrixEQTL R package
print(mtrql.SlicedData)
Generator for class "SlicedData":
Class fields:
Name: dataEnv nSlices1 rowNameSlices
Class: environment numeric list
Name: columnNames fileDelimiter fileSkipColumns
Class: character character numeric
Name: fileSkipRows fileSliceSize fileOmitCharacters
Class: numeric numeric character
Class Methods:
"Clear", "show#envRefClass", "nSlices", "getRefClass", "export",
"initialize", "CombineInOneSlice", "callSuper", "initFields", "nCols",
"getClass", "RowStandardizeCentered", "import", "SaveFile", "RowReorder",
"setSlice", "getSlice", "RowReorderSimple", "CreateFromMatrix", "nRows",
"ResliceCombined", "LoadFile", "ColumnSubsample", "SetNanRowMean",
"setSliceRaw", "getSliceRaw", "copy", "RowMatrixMultiply", "usingMethods",
"GetAllRowNames", "RowRemoveZeroEps", "field", ".objectParent",
"IsCombined", "untrace", "trace", "Clone", "GetNRowsInSlice",
".objectPackage", "show", "FindRow"
Reference Superclasses:
"envRefClass"
I want to access for instance class field say fileDelimiter and also class Methods say LoadFile but I couldn't, here is also my attempt to access class method LoadFile and the error message that generated:
# If I try to run this without "()"
data = mtrql.SlicedData
load_my_file = data.LoadFile(file)
data = data.LoadFile(file)
AttributeError: 'DocumentedSTFunction' object has no attribute 'LoadFile'
# And that's my attempt for when adding "()" to the class name
data = mtrql.SlicedData
load_my_file = data.LoadFile(file)
data = data.LoadFile(file)
AttributeError: 'RS4' object has no attribute 'LoadFile'
I tried to look for a solution to this issue but I wasn't successful, please help me understand and solve this issue.
Thank you so much in advance.

Answer 1

mtrql.SlicedData is a "Generator", that is a constructor. In R that means a function (that will return an instance of the class), which is why mtrql.SlicedData is an R function with rpy2.
Consider the following example from the R documentation (https://rdrr.io/r/methods/Introduction.html):
import rpy2.robjects as ro
Pos = ro.r("""
setClass("Pos", slots = c(latitude = "numeric", longitude = "numeric",
altitude = "numeric"))
""")
With rpy2, the object Pos is an R function:
>>> type(Pos)
rpy2.robjects.functions.SignatureTranslatedFunction
However that function object has an S3 class in R (there are several OOP systems in R, 2 of them coexisting in standard R unfortunately).
>>> tuple(Pos.rclass)
('classGeneratorFunction',)
A specific print function is implemented for this S3 class, and it will use the attributes package and className for the object (the R function-that-is-in-fact-a-Generator) to display all the info about the clas you are seeing.
Since this is a constructor, to create an instance you can do:
pos = Pos()
or
pos = Pos(latitude=0, longitude=0, altitude=-10)
The instance will have instance attributes (and methods)
>>> tuple(pos.list_attrs())
('latitude', 'longitude', 'altitude', 'class')
>>> tuple(pos.do_slot('altitude'))
(-10,)
With your specific example, you probably want something like:
slidata = mtrql.SlicedData()
slidata.do_slot('LoadFile')(file)
The documentation can provide more information about R S4 classes in rpy2, and how to make wrapper classes in Python that map attributes and methods.
https://rpy2.github.io/doc/v3.3.x/html/robjects_oop.html#s4-objects