coursera air pollution assignment

Question

Using Mac OS 10.10.3 RStudio Version 0.98.1103

My working directory is a list of 332 .csv files and I set it correctly. Here's the code:

pollutantmean <- function(directory, pollutant, id = 1:332) {
  all_files <- list.files(directory, full.names = T)
  dat <- data.frame()
  for(i in id) {
    dat <- rbind(dat, read.csv(all_files[i]))
  }
  ds <- (dat[, pollutant], na.rm = TRUE)
  mean(ds[, pollutant])
}

Part of the assignment is to get the mean of the first 10 numeric values of a pollutant. To do this, I used the call function (where "spectata" is the directory with 332 .csv files):

pollutantmean(specdata, "Nitrate", 1:10)

The error messages I get are:

**Error in file(file, "rt") : cannot open the connection

** In addition: Warning message: In file(file, "rt") : cannot open file 'NA': No such file or directory

Like many students that have posed questions here, I’m new to programming and to R and still distant from getting any results when calling my function. There are many questions and answers about this coursera assignment in stack overflow but my review of these exchanges hasn't addressed the bug in my code.

Anyone have a suggestion how to fix the bug?

Answer 1

In addition to the other answers is you can try this:

all_files <- list.files(directory, pattern="*.csv", full.names = TRUE)

to avoid select any other kind of file.

or even this strange one

all_files <- paste(directory, "\\", sprintf("%03d", id), ".csv", sep="")