How to use the lambda argument of smooth.spline in RPy WITHOUT Python interprating it as lambda

Question

I want to use the natural cubic smoothing splines smooth.spline from R in Python (like som many others want as well (Python natural smoothing splines, Is there

Answer 1

Perhaps you could use rpy2's Function.rcall() method when calling smooth.spline?

import rpy2.robjects as robjects
r_y = robjects.FloatVector(y_train)
r_x = robjects.FloatVector(x_train)

r_smooth_spline = robjects.r['smooth.spline']
args = (('x',r_x), ('y',r_y), ('lambda',42)) # pattern (('argname', value),...)

# import R's "GlobalEnv" to evaluate the function
from rpy2.robjects import globalenv

spline1 = r_smooth_spline.rcall(args, globalenv)

Answer 2

This little trick will work around the specific problem you're having, by allowing you to write "lambda" in a string.

kwargs = {"x": r_x, "y": r_y, "lambda":  42}
spline1 = r_smooth_spline(**kwargs)

In the general case, you can pass around argument containers easily with tuples and dicts.

# as normal
f = function("foo", "bar", my_kwarg="my_value")

# the same call using argument containers
args = ("foo", "bar")
kwargs = {"my_kwarg": "my_value"}
f = function(*args, **kwargs)

Answer 3

You can use Python's **<dict> in a function call to specify R named arguments that have a name that is not syntactically valid in Python.

See the documentation for more details: https://rpy2.github.io/doc/v3.2.x/html/robjects_functions.html