Statistics Study Notes: Generating and Manipulating Data in R, Assignments of Statistics

Download Statistics Study Notes: Generating and Manipulating Data in R and more Assignments Statistics in PDF only on Docsity! STAT 324 Discussion #2 TA Jiale Xu Office 1245D MSC Phone 262-5767 Email xujiale@stat.wisc.edu Office hour Tue. 2:10-3:20pm and Wed. 2:10-3:00pm 1 Generating Data 1.1 Combining Values into a Vector or List c(...) is used to define vectors. > height <- c(1.8, 1.90, 1.74, 1.75) > height [1] 1.80 1.90 1.74 1.75 1.2 Generating Equidistant series of numbers seq() generates regular sequences. > seq(3, 9) [1] 3 4 5 6 7 8 9 > seq(3, 9, by = 2) [1] 3 5 7 9 1.3 Sequential Function ”:” seq(1:9) can also be written using a special syntax > 3:9 [1] 3 4 5 6 7 8 9 1.4 Replicating Elements of Vectors rep() can generate repeated values. > rep(1:4, 2) [1] 1 2 3 4 1 2 3 4 > rep(1:4, c(2,2,2,2)) [1] 1 1 2 2 3 3 4 4 1 1.5 Generating Random Samples sample() takes a sample of the specified size from the elements of x using either with or without replacement. The general form is: sample(x, size, replace = FALSE, prob = NULL) > sample(1:10,8) [1] 5 4 9 1 2 8 10 6 By default size is equal to length(x) so that sample(x) generates a random permutation of the elements of x (or 1:x). > sample(1:10) [1] 6 1 3 2 5 7 8 10 4 9 Note that by default the sampling is without replacement. To generate sample with replacement, we need to add the argument ”replace = TRUE”. > sample(1:10,20,replace = TRUE) [1] 3 6 4 1 3 2 2 3 1 8 5 3 2 2 10 5 7 2 5 9 Example: > die1 <- sample(1:6, 100, replace = TRUE) > xtabs(~ die1) die1 1 2 3 4 5 6 21 20 16 14 16 13 > barchart(xtabs(~ die1)) 2 Operations on Vectors 2.1 Arithmetic Operations > x <- c(3, 8, 2) > y <- c(6, 7, 5) > 2*x [1] 6 16 4 > x^2 [1] 9 64 4 > x+y [1] 9 15 7 > x*y [1] 18 56 10 > x/y [1] 0.500000 1.142857 0.400000 > sum(x) 2