Sum the missing values from a data.frame
Examples
sum_missing(data.frame(a = c(1, 2), b = c(3, 4)))
#> data.frame(a = c(1, 2), b = c(3, 4)) has 0 missing values.
sum_missing(data.frame(a = c(1, NA), b = c(3, 4)))
#> data.frame(a = c(1, NA), b = c(3, 4)) has 1 missing values.
sum_missing(data.frame(a = c(1, NA), b = c(NA, 4)))
#> data.frame(a = c(1, NA), b = c(NA, 4)) has 2 missing values.
sum_missing(data.frame(a = c(NA, NA), b = c(NA, NA)))
#> data.frame(a = c(NA, NA), b = c(NA, NA)) has 4 missing values.