Convert of occurences of pattern in dataframe cells to other pattern

convert_from_to.R

# example dataframe
b <- structure(list(Sepal.Length = c("-", "-", "-", "4.6", "5", "5.4"
), Sepal.Width = c("3.5", "-", "-", "3.1", "3.6", "3.9"), Petal.Length = c("1.4", 
                                                                           "1.4", "-", "-", "1.4", "1.7"), Petal.Width = c(0.2, 0.2, 0.2, 
                                                                                                                           0.2, 0.2, 0.4), Species = structure(c(1L, 1L, 1L, 1L, 1L, 1L), .Label = c("setosa", 
                                                                                                                                                                                                     "versicolor", "virginica"), class = "factor")), row.names = c(NA,                                                                                                                                                                                                                                                          6L), class = "data.frame")
# function  
convert_all_to_from <- function(data, from, to) {
    clean <- data.frame(lapply(data, function(x) {gsub(from, to, x)}))
    return(clean)
}

# example command
convert_all_to_from(data = b, 
                    from = "-", 
                    to   = NA)