argument is not numeric or logical: returning NA in R

Question

I am trying to write a function to calculate the mean of a column. The function has the arguments directory and column_name. However, I keep getting the error "argument is not numeric or logical: returning NA":

pollutantmean <- function(directory, pollutant) {

    directoryVal <- directory
    pollutantVal <- pollutant

    pollutantData <- read.csv(directoryVal)
    meanVal <- mean(pollutantData$pollutantVal, na.rm = TRUE)

}

I called it by:

pollutantmean("001.csv", "nitrate")

"nitrate" is one of the column names.

Note that the following works, so I'm not sure why it's not working in my function:

mydata <- read.csv("001.csv")
mean(mydata$nitrate, na.rm = TRUE)

Please help. Thank you.

Solution 1

You should try meanVal <- mean(pollutantData[pollutantVal], na.rm = TRUE), indeed your data frame pollutantData doesn't have any column call pollutantVall, so you have pollutantData$pollutantVal which is NULL. If you wan to access to a data frame column using a character, you have to use the square brackets.

Solution 2

I'd like to add a correction. It should actually be

meanVal <- mean(pollutantData[,pollutantVal], na.rm = TRUE)

Note the , before the pollutantVal since pollutantVal is a column and needs to be indexed as such.