STAT 220: Basic Statistics for Quantitative Students

1. Write a function called addseq. It should take a single argument, a vector of length 3. It should add the vector c(1, 2, 3) to its argument and return the result. Sample output:

   > x=c(6,3,9)
   > addseq(x)
   [1]  7  5 12
   

   Hint: This function can be written using only a single argument.

   Answer:
   addseq = function(a) c(1,2,3)+a

2. Write a function called reverse. It should take a single argument, a vector of arbitrary length. It should then return the vector with its order reversed. Sample output:

   > x=c(1, 2, 8:4)
   > x
   [1] 1 2 8 7 6 5 4
   > reverse(x)
   [1] 4 5 6 7 8 2 1
   

   Hint: Use the length function and the seq function. You will also need the material in the "Optional: Indexing" section starting on page 17.

   Answer:
   reverse = function(a) a[length(a):1]

3. Write a function called addmulthyp. It should take two arguments, say x and y, and return a vector containing three elements: their sum, their product, and the length of the hypotenuse of a right triangle with legs x and y. Sample output:

   > addmulthyp(3,4)
   [1]  7 12  5
   > addmulthyp(1,1)
   [1] 2.000000 1.000000 1.414214
   

   Hint: Use the sqrt function. Look up its help file if you need to.

   Answer:
   addmulthyp = function(x, y) c(x+y, x*y, sqrt(x^2+y^2))

4. Write a function called tableplot. It should take one argument. The argument will be a data.frame with columns named "volumes" and "expend", like the "a" object shown at the bottom of page 12. The function should produce a scatterplot of these two columns. The x-axis should be labeled "volumes" and the y-axis should be labeled "expend". The title of the plot should read "volumes vs. expend". Sample output:

   > a = read.csv("univ-libraries.csv")
   > tableplot(a)
   

   

Answer:
tableplot = function(x) plot(x[,"volumes"], x[,"expend"], xlab="volumes", ylab="expend", main="volumes vs. expend")

If you want to look at some example R functions, check out the files rcompfunctions.r and dice.r in this directory.