napalm.R

library(purrr)
library(dplyr)

na_set <- function(x, p){
  p <- as_mapper(p)
  x[p(x)] <- NA
  x
}

# or something like this using case_when
# na_set <- function(x, p){
#   p  <- as_mapper(p)
#   na <- as(NA, typeof(x))
#
#   case_when(
#     p(x) ~ na,
#     TRUE ~ x
#   )
# }

# > a <- c(NA, letters[1:5] )
# > na_set(a, ~. == "a")
# [1] NA  NA  "b" "c" "d" "e"


napalm_all <- function(data, p){
  mutate_all(data, funs(na_set(., p)) )
}

napalm_at <- function(data, at, p){
  mutate_at(data, at, funs(na_set(., p)) )
}

napalm_if <- function(data, test, p){
  mutate_if(data, test, funs(na_set(., p)) )
}

a <- c(NA, letters[1:5] )
na_set(a, ~. == "a")

small <- airquality %>%
  slice(1:10)

# set NA in all columns when the variable is < 20
napalm_all( small, ~ . < 20 )

# set NA only for these variables, using the tidy select
# notation given for free by mutate_at
napalm_at( small, vars(Ozone:Wind), ~ . < 20 )

# same for the if variant, using mutate_if
napalm_if( small, is.numeric, ~ . < 20)