These questions are based on Alex’s concept map about looping in R.
Beginner or Competent
1) What function would one use to loop and apply a function over elements in the following object in R: vec <- list(“test”, “grade”, “score”)?
2) Write a for loop in R, which prints every element of the following object if the element in greater than 5? Vec <- c(1:10)
Here I would be looking more that they are capable of understanding the basic workings of loops and loop functions. In Q1, the ‘lapply’ function would be used because the object is a list and they would need to know that ‘apply’ families loop through elements of an object and apply a function and they would need to be familiar with these functions. Q2 just tests whether they understand how to use the loop function for a particular problem.
Competent or Expert
1) What is the most efficient way to loop and apply a function over an object that contains 600,000 elements in R?
2) Write a function that reads files in a directory and for each file it summarizes the mean and standard deviation for each of the numeric variables in the file.
In Q1, I would anticipate an expert to identify the scale of the problem (even if rather simple) and understand that apply functions are more efficient for this task compared to making a standard loop. in Q2, this is a much more difficult task and experts would tackle this quickly and would make the looping within the function easier and simpler with fewer lines of code. I would recognize this by the differences in their use of apply functions and nested loops.
Although these don’t necessarily get an “why” one would do things, which would better characterize an expert from a competent practitioner, I think I would be looking more for ‘experts’ to identify faster more efficient ways of looping, which create cleaner and simpler to read code.