apply_merge.R

#' Apply and Merge
#'
#' Applies the given function to each row of the data frame. The function is
#' expected to return a data frame itself. The resulting data frames are bound
#' together and joined with the previous data frame.
apply_merge <- function (df, f, cols) {
    # We first need to label the rows in the given data frame. We use a column
    # name with period as this is an implementation detail.
    df$.id <- 1:nrow(df)
    
    # The function gets applied to  the given columns. Since the user has
    # specified them as strings, we need to retrieve those from the given data
    # frame.
    call <- c(list(f), lapply(cols, function (col) df[[col]]), list(SIMPLIFY = FALSE))
    applied <- do.call(mapply, call)
    
    # Each of the resulting data frames need to be labelled with the index
    # column as well in order to allow for a join later.
    for (id in 1:nrow(df)) {
        applied[[id]]$.id <- id
    }
    
    # All intermediate data frames are combined.
    bound <- do.call(rbind, applied)
    
    # We join these together with the orignal data frame.
    joined <- dplyr::inner_join(df, bound, by = '.id')
    
    # The index column is no longer needed and deleted.
    joined$.id <- NULL
    
    return(joined)
}