Function to count NA values at each level of a factor

Question

I have this dataframe:

set.seed(50)
data <- data.frame(age=c(rep(\"juv\", 10), rep(\"ad\", 10)),
                   sex=c(rep(\"m\", 10), rep(\"f\", 10)),         


        

Answer 1

Use aggregate:

nacheck <- function(var, factor)
    aggregate(var, list(factor), function(x) sum(is.na(x)))

nacheck(data$length, data$age)
nacheck(data$length, data$sex)
nacheck(data$length, data$size)

You could also apply this to your dataframe, by each factor to get NA counts for all of the dimension measures for each factor.

apply(data[,c("length","width","height")], 2, nacheck, factor=data$age)
apply(data[,c("length","width","height")], 2, nacheck, factor=data$sex)
apply(data[,c("length","width","height")], 2, nacheck, factor=data$size)

To do this all as one function, nest nacheck in something and then lapply:

exploreNA <- function(df, factors){
    nacheck <- function(var, factor)
        aggregate(var, list(factor), function(x) sum(is.na(x)))
    lapply(factors, function(x) apply(df, 2, nacheck, factor=x))
}

exploreNA(data[,c("length","width","height")], list(data$age, data$sex, data$size))