STA 248 S: Some R Basics

Transcription

1 STA 248 S: Some R Basics The real basics The R prompt > > # A comment in R. Data To make the variable x equal to 2 use > x <- 2 or > x = 2 To make x a vector, use the function c() ( c for concatenate) > x = c(1,2,3,4) The 3rd entry of x > x[3] > x[3] = 7 Comparison and logical operators > x >= 2 > x!= 2 > x[x!=2] > x==2 > x==2 x==3 > x==2 & x==3 Counts > sum(x >= 2) Shortcuts > x = 1:4 > y = rep(c(2,3),4) 1

2 Character variables > xnames = c("jack","jill","dick","jane") > names(x) = xnames > x > x["jill"] Matrices > mymatrix = matrix(x,ncol=2) > mymatrix = matrix(x,ncol=2,byrow=t) > mymatrix[2,1] > mymatrix[1,] Lists > l = list(a=7, b=matrix(1:4,2,2), c=c(3,7)) > l > l$a > l$b > l$c Operators Addition: + Subtraction: - Multiplication: * Division: / Exponentiation: ** or ˆ If variables being added together are vectors of equal length or are matrices with equal dimensions, R will do elementwise addition. That is, the first elements of the two vectors will be added to one another, the second elements will be added togther, and so on. The result will be a vector (or matrix) with the same dimensions as the original vectors (or matrices). This also applies to subtraction, multiplication and division. Matrix multiplication > matrix1 %&% matrix2 2

3 Functions Function abs(x) apply(m,2,function) cbind(x1, x2) rbind(x1, x2) exp(x) length(x) log(x) log10(x) sort(x) sqrt(x) sum(x) Use absolute value applies a function to each column of the matrix m (what happens if the 2 is replaced by a 1?) forms a matrix whose columns are the vectors x1, x2 forms a matrix whose rows are the vectors x1, x2 e x length; if x is a vector or a matrix you are given the total number of elements in x natural log (ln) base 10 log x sorted from smallest to largest square root the sum of all of the elements of x Missing values The missing value indicator in R is NA (not available). Operations on missing values produce missing values. For example > mydata = c(2,4,5,na) > mean(mydata) > mean(mydata, na.rm=t) Getting help Help for the function apply > help(apply) >?apply Open a web browser to the R manuals > help.start() Find functions whose help pages include the word regression > help.search(keyword="regression") Running a previously stored R program Run the R commands stored in the text file filename.r > source("filename.r") Reading data into R Numerical data only > mydata = matrix(scan("fakedata.txt"),ncol=3,byrow=t) 3

4 Create a dataframe > mydata = read.table("fakedata2.txt",head=t) > attach(mydata) > replace(variablename, variablename==999, NA) Graphics On one page print 6 plots in 2 rows and 3 columns > par(mfrow=c(2,3)) Some other things The last answer >.Last.value List all of your variables > ls() Remove x > rm(x) Change number of significant digits to 3; default is 7. > options(digits=3) Saving your work in Windows Under File, Save Workspace will create a file with extension RData which will save all of your variables. Save to File will create a text file of what is in your R Console. Plots can be printed and saved by right-clicking on them or by choosing the appropriate option under File when the graphics window is active. Using R on Cquest Your files are stored on a Linux server and are available from any Cquest lab or by remote access using ssh. Ramsey Wright labs (107/109 and 211): The operating system is Windows XP. R is under Statistics Applications in the Start menu. To quit R, chose Exit under File. Your home folder is the H: drive. To logout look under Start. For a web browser, Firefox is an icon on your desktop. 4

5 Earth Sciences lab (1046): The operating system is Linux. R is available under Applications > Cquest. To logout look under Start. For a web browser, Firefox is the mouse on a globe icon beside Desktop. To quit R > q() Saving graphs: > pdf("filename.pdf", paper="letter") > plot(mydata) > dev.off() To save what you see in your R workspace in a text file, open an editor in another window and cut and paste what you want to keep. To save your variables, select y when prompted to save workspace image on exiting R. 5

6 Assignment for next class 1. If you re going to use R on your own computer, download and install it. If you re going to use R on Cquest, get a Cquest account. 2. Run the following commands and figure out what they do. > y = rnorm(50,1,4) > hist(y) > mean(y) > sqrt(var(y)) 3. Bring to next class: A printed plot created by the above commands. A printed file containing the commands and the numerical output for the above commands that return a number. (This assignment will not be graded!) 6