Slicing Data and Calculating Means in R

These questions are based on the lesson Analysing patient data from Programming with R.

Question 1

Consider the following dataframe (dat):

Which code would correctly return the value 38.

1. dat[3, 2]
2. dat[c(3, 2)]
3. dat[2, 3]
4. dat[3:2]

Question 2

Which code would give a mean value for each of the rows in dat

1. apply(dat, 1, mean)
2. apply(dat, 2, mean)
3. rowMeans(dat)
4. 1 and 3
5. 2 and 3

Answers to question 2:

1. Student does not realise that rowMeans(dat) does the same as apply(dat, 1, mean).
2. Student has mixed the value for rows and columns in the MARGIN argument, and has not considered rowMeans.
3. Student does not realise that apply(dat, 1, mean) also retrieves the row means.
4. Correct answer.
5. Student has mixed the value for rows and columns in the MARGIN argument.