Function to divide a data.frame by unique values of a column

divide.R

# Divide a Data Frame or Matrix Into Subsets
# @param obj a data.frame or matrix to be split into subsets, divided by the
# categorical variable
# @param by a character-string, specifying the column to subset
# @return a list, containing the subsetted data sets. The names of the list
# correspond to the value of the subsetted list
divide <- function (obj, by) {
  # Get the set of possible values
  column.levels <-if (is.factor(obj[, by])) {
    levels(obj[, by])
  } else {
    unique(obj[, by])
  }
  # A list used to store each individual data.frame
  res <- list()
  # Iterate through all possible values and store each subset in a separate
  # entry in the list
  for (val in column.levels) {
    # Determine which rows match this value
    hits <- obj[, by] == val
    # Store data set temporarily in a local value
    data.set <- obj[hits, ]
    # Assign levels to the column. This adds levels to string data.
    levels(data.set[, by]) <- column.levels
    # Store data set in list
    res[[val]] <- data.set
  }

  # Return list
  res
}

You can use dplyr::group_split() for this functionality. Here is the link to the documentation
https://dplyr.tidyverse.org/reference/group_split.html