Calling marginaleffects in functions, loops,
environments, or after re-assigning variables
Functions from the marginaleffects package can sometimes
fail when they are called inside a function, loop, or other
environments. To see why, it is important to know that
marginaleffects often needs to operate on the original data
that was used to fit the model. To extract this original data, we use
the get_data() function from the insight
package.
In most cases, get_data() can extract the data which is
stored inside the model object created by the modeling package. However,
some modeling packages do not save the original data in the
model object (in order to save memory). In those cases,
get_data() will parse the call to find the name of the data
object, and will search for that data object in the global environment.
When users fit models in a different environment (e.g., function calls),
get_data() may not be able to retrieve the original
data.
A related problem can arise if users fit a model, but then assign a new value to the variable that used to store the dataset.
Recommendations:
- Supply your dataset explicitly to the
newdataargument ofslopesfunctions. - Avoid assigning a new value to a variable that you use to store a dataset for model fitting.