Sample Exam Questions

• The following regular expression is meant to find a string containing dollars and cents where the cents are optional:
  grep("\\$[0-9]*\\.[0-9]{2}", x)
  Find three such character strings that are not handled by this regular expression.

• For the bank database used in class (tables would be provided), describe the results table from the following query:
  SELECT CustNo, SUM(Balance) FROM Reg R, Acct A WHERE A.No = R.AcctNo GROUP BY A.Branch ;

• How would you generate a pseudo-random number using the accepatnce rejection method from the following distribution. Give your answer in pseudo-code with sketches.
  f(x) = (3/4)(1 - x^2)
  for -1 < x < 1, and 0 otherwise.

• Describe the following graphic using Wilkinson's Grammar of Graphs:

  

• Correct the following malformed XML:
  <?xml version="1.0" ?>
  <country>
    <state>
     <gml:name abb=AZ>Arizona</gml:name>
      <county>
       <gml:name>Apache</gml:name>
       <gml:location>
        <Point>
         <gml:coord> <gml:X>-109</gml:X><gml:Y>35</gml:Y></gml:coord>
        </point>
       </gml:location>
      </county>
      <county>
       <gml:name>Cochise</gml:name>
       <gml:location>
        <Point>
         <gml:coord> <gml:X>-109</gml:X><gml:Y>31</gml:coord>
        </Point>
       </gml:location>
      </county>
     </state>
    </country>

• Rewrite the following for-loop using one of the apply functions.
  for (i in 1:length(files) {
    newMsg[[i]] = readLines(paste(x,files[i],sep"/"))
    newMsg[[i]] = cleanMsg(newMsg[[i]])
  }

• Given the handler function below for the xmlTreeParse, describe what is being collected.
  linkHandlers = function()
  {
    n = ""
    a = function(x){
     href = xmlGetAttr(x, "href")
      if(!is.null(href)) n <<- c(n, href)
    }
    list(a = a, .value = function() n)
  }

• Use vector operations to simplify the following:
  percentSpam = function(file) {
    totalCount = 0
    spamCount = 0
    for (i in file) {
     if (substr(i, 1, 1) == "s" {
      spamCount = spamCount + 1
     }
    totalCount = totalCount + 1
    }
  }