I'm using the MissRanger package in R to perform imputation on a very large dataset. While the package documentation clearly explains the iterative random forest imputation process, I couldn't find explicit details regarding how MissRanger initializes missing values before starting the iterations.
My intuition, based on reading the documentation, suggests that MissRanger might be using the imputeUnivariate() method as this is part of the MissRanger package. imputeUnivariate() is described as:
Fills missing values of a vector, matrix or data frame by sampling with replacement from the non-missing values. For data frames, this sampling is done within column.
Could someone clarify how MissRanger initializes the imputation process?