Replace empty by na
Examples
airquality[which(is.na(airquality$Ozone)), "Ozone"] <- ""
empty_as_na(airquality$Ozone)
#> [1] "41" "36" "12" "18" NA "28" "23" "19" "8" NA "7" "16"
#> [13] "11" "14" "18" "14" "34" "6" "30" "11" "1" "11" "4" "32"
#> [25] NA NA NA "23" "45" "115" "37" NA NA NA NA NA
#> [37] NA "29" NA "71" "39" NA NA "23" NA NA "21" "37"
#> [49] "20" "12" "13" NA NA NA NA NA NA NA NA NA
#> [61] NA "135" "49" "32" NA "64" "40" "77" "97" "97" "85" NA
#> [73] "10" "27" NA "7" "48" "35" "61" "79" "63" "16" NA NA
#> [85] "80" "108" "20" "52" "82" "50" "64" "59" "39" "9" "16" "78"
#> [97] "35" "66" "122" "89" "110" NA NA "44" "28" "65" NA "22"
#> [109] "59" "23" "31" "44" "21" "9" NA "45" "168" "73" NA "76"
#> [121] "118" "84" "85" "96" "78" "73" "91" "47" "32" "20" "23" "21"
#> [133] "24" "44" "21" "28" "9" "13" "46" "18" "13" "24" "16" "13"
#> [145] "23" "36" "7" "14" "30" NA "14" "18" "20"