####read in the data####

###CSV file###

grades_data <- read.csv("K:/teaching/misc_presentations/PubH_7440_spring2011/20110127/grades_example.csv", header = T)

###tab delimited file###

grades_data <- read.table("K:/teaching/misc_presentations/PubH_7440_spring2011/20110127/grades_example.txt", header = T)

###Data manipulation example###

###determine each students homework average###

grades_data$hwk_avg <- (grades_data$hwk_1 + grades_data$hwk_2 + grades_data$hwk_3 + grades_data$hwk_4 + grades_data$hwk_5)/5

###determine each students homework average using the built-in function rowMeans###

grades_data$hwk_avg2 <- rowMeans(grades_data[,c("hwk_1", "hwk_2", "hwk_3", "hwk_4", "hwk_5")])

###determine homework average percent###

grades_data$hwk_pct <- grades_data$hwk_avg/20 * 100

###determine basic summary statistics for each exam###

###test 1###

###mean score###

mean(grades_data$test_1)

###standard deviation###

sd(grades_data$test_1)

###5 number summary (min, 25%, 50%, 75%, max)###

quantile(grades_data$test_1, c(0, .25, .5, .75, 1))

###test 2###

###mean score###

mean(grades_data$test_2)

###standard deviation###

sd(grades_data$test_2)

###5 number summary (min, 25%, 50%, 75%, max)###

quantile(grades_data$test_2, c(0, .25, .5, .75, 1))

###basic graphical summaries###

###makes plots 2 by 2###

par(mfrow = c(2,2))

###histogram for test 1###

hist(grades_data$test_1)

###histogram for test 2###

hist(grades_data$test_2)

###plot scatterplot for test 1 and test 2###

plot(grades_data$test_1, grades_data$test_2, xlim = c(40,100), ylim = c(40,100), xlab = "Test 1 Score", ylab = "Test 2 Score")

###function to calculate each student's overall course grade###

calc_grade <- function(hwk, test1, test2) {

###calculate the overall percentage for the course###

course_pct <- round(hwk * .4 + test1 * .3 + test2 * .3, 0)

###create a vector to store course grades###

course_grade <- rep(NA, length(course_pct))

###loop to calculate grades###

for(i in 1:length(course_pct)) {

if(course_pct[i] > 85) { 

course_grade[i] <- "A" 

} else if(course_pct[i] > 80) {

course_grade[i] <- "B" 

} else {

course_grade[i] <- "C"

}

}

return(cbind(course_pct, course_grade))

}

###calculate final grades###

final_grades <- calc_grade(hwk = grades_data$hwk_pct, test1 = grades_data$test_1, test2 = grades_data$test_2)

###add final grades to the grades data set###

grades_data <- cbind(grades_data, final_grades)

###miscellanious###

###help###

help('rowMeans')

###load a package###

library(MASS)

library(BRugs)