impute a included NA valiable.

impute.r

library(dplyr)

data <- data_frame(var = c(0, NA, 2))
data %>% mutate(var = coalesce(var, 1))
data %>% mutate(var = replace(var, which(is.na(var)), 1))
data %>% mutate(var = if_else(is.na(var), 1, var))
# A tibble: 3 × 1
# var
# <dbl>
# 1     0
# 2     1
# 3     2