# a brief introduction to some R commands

 # learn about R, download R from http://www.r-project.org/

 # there are many nice R introductions on the web, one that I like is at:  http://www.statmethods.net/index.html



ls()     # shows the objects in the current workspace

name <- c("Hamb","Chsbrg","Delxbg","Fish","Chix")    # create a new object

sizeg <- c(107, 121, 216, 156, 223)

totfat <- c(9, 13, 31, 25, 20)

burgers <- data.frame(Name=name,sizeg,totfat)    # create a data frame

rm(name, sizeg, totfat)    # remove objects when they are not needed

burgers          

plot(burgers$sizeg,burgers$totfat,xlab="total size",ylab="fat",main="Size vs fat")

    # the $ sign is used to identify a variable in a data frame

summary(burgers)



  # here we read in data from a file

burgers2 <- read.table("c:/temp/burgs1.txt",header=T)


  # here we read in a comma-separated value (CSV) file saved from Excel

student1 <- read.csv("c:/temp/student2.csv",na.strings = ".",header=T)

student1

plot(student1$Dias1,student1$Sys1)     # Note that objects are case-sensitive

table(student1$Eye)

table(student1$Eye,student1$Thumb)

tapply(student1$Sys1,student1$Eye,mean)  
    # calculates the mean value for Sys1 separately for each value of Eye