After referring documentations in R and github, below points I have considered as the limitation
•In order to work with Keras in Rstudio, R matrices and arrays are marshaled to python to convert them to NumPy arrays.
•Implies that the NumPy array will be Fortran-ordered(default in R), rather than C-ordered which is default for NumPy library.
•In the case of Keras training, between shuffling, drawing batches, copying to the GPU/CPU, and 10 epochs there are a ton of accesses to the Fortran-ordered array which add up to a ~ 40% performance penalty.
•The performance penalty causes R to consume more time than Python.
•Deep learning models can be implemented in R as well, with the cost of time.