R Histogram & Boxplot of Grades

--D. Thiebaut (talk) 10:45, 22 March 2015 (EDT)

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This is a simple recipe for generating a histogram and boxplot of student grades. For a much fancier solution, please see the R ProfessR package created and maintained by Prof. Jonathan M. Lees at UNC.

Data

The grades are saved in a txt file, 1 grade per line. Here's a typical list

R Script

# set working directory 
setwd( "/Users/thiebaut/Desktop/Dropbox/111/" )

# read the grades, 1 per line, and make grades numeric
g <- read.table( "midtermGrades.txt" )
gg <- sapply( g, as.numeric)

# create a layout with boxplot at bottom
nf <- layout( mat = matrix(c(1,2),2,1, byrow=TRUE),  height = c(3,1))
# set parameters
par( mar=c(3.1, 3.1, 1.1, 2.1) )

# display histogram
hist <- hist( gg, main="Histogram of Midterm", col="lightgreen", breaks=17, xaxt='n')
axis(2)
axis(side=1, at=seq( 20,100,5))

# display boxplot
B <- boxplot( gg, horizontal=TRUE, outline=TRUE, frame=FALSE, col="green", notch=TRUE, width=40)

Output