Calculate the mean of one column from several CSV files

Question

I have over 300 CSV files in a folder (named 001.csv, 002.csv and so on). Each contains a data frame with a header. I am writing a function that will take three arguments: t

Answer 1

You do not need more functions. The solution can be simpler from my understanding in 6 lines:

pollutantmean <- function(directory, pollutant, id = 1:10) {
filenames <- sprintf("%03d.csv", id)
filenames <- paste(directory, filenames, sep="/")
ldf <- lapply(filenames, read.csv)
df=ldply(ldf)
# df is your list of data.frames
mean(df[, pollutant], na.rm = TRUE)
}