### Basic R Programming

R is a very flexible and powerful programming language, as well as a package that is written using that language (and others like C). The following program demonstrates many of its basic features. You can cut and paste it into R, or download the file that includes it from here. If you run it line by line, many of its features will become clear. Both editions of *R for SAS and SPSS Users* and *R for Stata Users* work through a version of this program line-by-line, showing the output and explaining what R is doing.

# Filename: ProgrammingBasics.R # ---Simple Calculations--- 2 + 3 x <- 2 y <- 3 x + y x * y # ---Data Structures--- # Vectors workshop <- c(1, 2, 1, 2, 1, 2, 1, 2) print(workshop) workshop gender <- c("f", "f", "f", NA, "m", "m", "m", "m") q1 <- c(1, 2, 2, 3, 4, 5, 5, 4) q2 <- c(1, 1, 2, 1, 5, 4, 3, 5) q3 <- c(5, 4, 4,NA, 2, 5, 4, 5) q4 <- c(1, 1, 3, 3, 4, 5, 4, 5) # Selecting Elements of Vectors q1[5] q1[ c(5, 6, 7, 8) ] q1[5:8] q1[gender == "m"] mean( q1[ gender == "m" ], na.rm = TRUE) # ---Factors--- # Numeric Factors # First, as a vector workshop <- c(1, 2, 1, 2, 1, 2, 1, 2) workshop table(workshop) mean(workshop) gender[workshop == 2] # Now as a factor workshop <- c(1, 2, 1, 2, 1, 2, 1, 2) workshop <- factor(workshop) workshop table(workshop) mean(workshop) #generates error now. gender[workshop == 2] gender[workshop == "2"] # Recreate workshop, making it a factor # including levels that don't yet exist. workshop <- c(1, 2, 1, 2, 1, 2, 1, 2) workshop <- factor( workshop, levels = c( 1, 2, 3, 4), labels = c("R", "SAS", "SPSS", "Stata") ) # Recreate it with just the levels it # curently has. workshop <- c(1, 2, 1, 2, 1, 2, 1, 2) workshop <- factor( workshop, levels = c( 1, 2), labels = c("R","SAS") ) workshop table(workshop) gender[workshop == 2] gender[workshop == "2"] gender[workshop == "SAS"] # Character factors gender <- c("f", "f", "f", NA, "m", "m", "m", "m") gender <- factor( gender, levels = c("m", "f"), labels = c("Male", "Female") ) gender table(gender) workshop[gender == "m"] workshop[gender == "Male"] # Recreate gender and make it a factor, # keeping simpler m and f as labels. gender <- c("f", "f", "f", NA, "m", "m", "m", "m") gender <- factor(gender) gender # Data Frames mydata <- data.frame(workshop, gender, q1, q2, q3, q4) mydata names(mydata) row.names(mydata) # Selecting components by index number mydata[8, 6] #8th obs, 6th var mydata[ , 6] #All obs, 6th var mydata[ , 6][5:8] #6th var, obs 5:8 # Selecting components by name mydata$q1 mydata$q1[5:8] # Example renaming gender to sex while # creating a data frame (left as a comment) # # mydata <- data.frame(workshop, sex = gender, # q1, q2, q3, q4) # Matrices # Creating from vectors mymatrix <- cbind(q1, q2, q3, q4) mymatrix dim(mymatrix) # Creating from matrix function # left as a comment so we keep # version with names q1, q2... # # mymatrix <- matrix( # c(1, 1, 5, 1, # 2, 1, 4, 1, # 2, 2, 4, 3, # 3, 1, NA,3, # 4, 5, 2, 4, # 5, 4, 5, 5, # 5, 3, 4, 4, # 4, 5, 5, 5), # nrow = 8, ncol = 4, byrow = TRUE) # mymatrix table(mymatrix) mean(mymatrix, na.rm = TRUE) cor(mymatrix, use = "pairwise") # Selecting Subsets of Matrices mymatrix[8, 4] mymatrix[5:8, 3:4] mymatrix[ ,4][1:4] mymatrix$q4 # No good! mymatrix[ ,"q4"] # Matrix Algebra mymatrixT <- t(mymatrix) mymatrixT # Lists mylist <- list(workshop, gender, q1, q2, q3, q4, mymatrix) mylist # List, this time adding names mylist <- list( workshop = workshop, gender = gender, q1 = q1, q2 = q2, q3 = q3, q4 = q4, mymatrix = mymatrix) mylist # Selecting components by index number. mylist[[2]] mylist[[2]][5:8] mylist[2] mylist[2][5:8] # Bad! # Selecting components by name. mylist$q1 mylist$mymatrix[5:8, 3:4] # ---Saving Your Work--- ls() objects() #same as ls() save.image("myall.RData") save(mydata, file = "mydata.RData") # The 2nd approach is commented to keep # the q variables for following examples. # rm(x, y, workshop, gender, q1, q2, q3, q4, mylist) # ls() # save.image(file = "mydata.RData") # ---Comments to Document Your Programs--- # This comment is on its own line, between functions. workshop <- c(1, 2, 1, 2, #This comment is within the arguments. 1, 2, 1, 2) #And this is at the end. # ---Comments to Document Your Objects--- comment(mydata) <- "Example data from R for SAS and SPSS Users" comment(mydata) # ---Controlling Functions--- # Controlling Functions with Arguments help("mean") mean(x = q3, trim = .25, na.rm = TRUE) mean(na.rm = TRUE, x = q3, trim = .25) mean(q3, .25, TRUE) mean(q3, t = .25, na.rm = TRUE) mean(1, 2, 3) mean( c(1, 2, 3) ) mean( 1:3 ) # Controlling Functions With Formulas lm( q4 ~ q1 + q2 + q3, data = mydata ) t.test(q1 ~ gender, data = mydata) t.test( q1[ which(gender == "Female") ], q1[ which(gender == "Male") ], data = mydata) # Data ignored! # Controlling Functions with Extractor Functions lm( q4 ~ q1 + q2 + q3, data = mydata ) myModel <- lm( q4 ~ q1 + q2 + q3, data = mydata ) class(myModel) summary(myModel) # How Much Output Is There? print(mymodel) mode(myModel) class(myModel) names(myModel) print( unclass(myModel) ) myModel$coefficients class( myModel$coefficients ) barplot( myModel$coefficients ) # ---Writing Your Own Functions (Macros)--- myvar <- c(1, 2, 3, 4, 5) # A bad function. mystats <- function(x) { mean(x, na.rm = TRUE) sd(x, na.rm = TRUE) } mystats(myvar) # A good function that just prints. mystats <- function(x) { print( mean(x, na.rm = TRUE) ) print( sd(x, na.rm = TRUE) ) } mystats(myvar) # A function with vector output. mystats <- function(x) { mymean <- mean(x, na.rm = TRUE) mysd <- sd(x, na.rm = TRUE) c(mean = mymean, sd = mysd ) } mystats(myvar) myVector <- mystats(myvar) myVector # A function with list output. mystats <- function(x) { myinput <- x mymean <- mean(x, na.rm = TRUE) mysd <- sd(x, na.rm = TRUE) list(data = myinput, mean = mymean, sd = mysd) } mystats(myvar) myStatlist <- mystats(myvar) myStatlist mystats save(mydata, mymatrix, mylist, mystats, file = "myWorkspace.RData")

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Looks like the “<" symbol is showing up as "<" in the code above. This would probably be confusing to a beginner.

hah, I mean that it is showing up as “& lt ;” with the spaces removed