R Programming Week 2 Solutions

My solutions to Exercises:

#1 (pollutantmean.R)

pollutantmean <- function(directory, pollutant, id=1:332){
        sum <- 0
        trueValues <- 0 
        for (i in id){
                prefix <- "";
                if (i<10)prefix <- "00"
                else if(i<100) prefix <- "0"
 
                path <- paste(directory, "\\", prefix, i, ".csv", sep="")
                ## print(path)
                data <- read.csv(path) 
                d <- data[[pollutant]] 
                d <- d[!is.na(d)]
 
                # if(i==1)print(d)
 
                sum <- sum + sum(d)
 
                trueValues <- trueValues + sum(!is.na(d))
#                 if(i==1){
#                         print(sum(d))
#                         print(sum)
#                         print(trueValues)
#                         print(sum/trueValues) 
#                 } 
#         print(sum/length(id))
        }
        sum/trueValues 
}

#2 (complete.R)

complete <- function(directory, id=1:332){
        fileNos <- c()
        numberOfElements <-c()
        for (i in id){
 
                prefix <- "";
                if (i<10)prefix <- "00"
                else if(i<100) prefix <- "0"
 
                path <- paste(directory, "\\", prefix, i, ".csv", sep="")
 
                data <- read.csv(path) 
                d1 <- data[["sulfate"]]   
                d2 <- data[["nitrate"]]
 
                good <- complete.cases(d1, d2) 
                bothNotNA <- length(good[good==TRUE])   
                fileNos <- c(fileNos, i)
                numberOfElements <- c(numberOfElements, bothNotNA) 
        }
        data.frame(id = fileNos, nobs = numberOfElements)
}

#3 (corr.R)

corr <- function(directory, threshold = 0){
        cors <- c() 
        for (i in 1:332){
 
                prefix <- "";
                if (i<10)prefix <- "00"
                else if(i<100) prefix <- "0"
 
                path <- paste(directory, "\\", prefix, i, ".csv", sep="")
 
                data <- read.csv(path) 
                d1 <- data[["sulfate"]]   
                d2 <- data[["nitrate"]]
 
                good <- complete.cases(d1, d2)
                bothNotNA <- length(good[good])  
                if(bothNotNA>threshold){
                        cors <- c(cors, cor(d1[good], d2[good]))
                }
        }
        if(length(cors)==0)vector(mode="numeric", length=0)
        else cors
}