DESCRIPTION

Students:  Please keep in mind the OMSI rules.  Save your files often,
make sure OMSI fills your entire screen at all times, etc.  Remember
that clicking CopyQtoA will copy the entire question box to the end of
the answer box.  

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Don't forget to FREQUENTLY save and submit your work, even work    
in progress.  The network may get busy at the end of the exam      
period, making it difficult to submit then.  The server will shut 
down at the appointed time, and NO further work will be accepted.

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In questions involving code which will PARTIALLY be given to you in the
question specs, you need to add new code.  There may not be information
given as to where the new cod should be inserted.  Do not modify the
lines already there unless instructed to do so.

If a question includes test code, make sure to INCLUDE IT IN YOUR
SUBMISSION.

IF YOU FINISH EARLY, please leave the exam room.  If you stay, close
your laptop and sit quietly.

QUESTION -ext .R -run 'Rscript omsi_answer1.R'

Consider R's built-in dataset 'faithful', a 2-column data frame whose
first few rows are

  eruptions waiting
1     3.600      79
2     1.800      54
3     3.333      74
4     2.283      62
5     4.533      85
6     2.883      55

The data are for the famous geyser, Old Faithful in Yellowstone National
Park.  The first column gives the duration of an eruption, and the
second has the time between that eruption and the previous one.

Write code to print (a) the number of eruptions of duration more than
3.25, and (b) the mean eruption duration among eruptions occurring after a
wait time of more than 65.  (Quantity (b) is motivated by the notion
that longer waits imply more water accumulates and thus longer
eruptions.)  For full credit, your code must be loopless.

print('number of durations > 3.25:')
print(             )
print('mean eruption duration for waits > 65:')
print(             )

QUESTION -ext .R -run 'Rscript omsi_answer2.R'

Write code to create a class 'vecPos', objects of which are vectors with
all positive elements.  Part of your code will be a function
'makeVecPos(x)' that inputs a plain vector x of all positive elements
and returns an object of class 'vecPos' (with the same elements); it
will report an error if the input is not all positive.  You will also
overload '>' so that one object of the class is considered greater than
another if and only if each element in the first object is greater than
the corresponding element in the second object.  For full credit, your
code must be loop-free.

Note: You may need to call as.vector() to convert your 'vecPos' object
to a plain vector.

makeVecPos <- function(x)
{


}

u <- c(5,12,13)
v <- c(1,88,8)
w <- c(2,11,11)
uvp <- makeVecPos(u)
vvp <- makeVecPos(v)
wvp <- makeVecPos(w)
print(uvp)
print(uvp > vvp)  # prints FALSE
print(uvp > wvp)  # prints TRUE

try:
  {
  z <- c(0,88,8)
  zvp <- makeVecPos(z)  # causes error, with msg "must be all-positive"
  # OMSI will report "Run unsuccessful," but don't worry :-)
  }