For loops in R

This lesson demonstrates how to analyze multiple data sets by sending them through a for loop.

Analyzing multiple data sets

Question 1

len <- 0
vowels <- c("a", "e", "i", "o", "u")
for (v in vowels) {
    len <- len + 1
}
len

Upon completion of the preceding loop, the value of the variable len will be:

1.  0
2.  1
3.  6
4.  5

Question 2

letter <- "z"
for (letter in c("a", "b", "c")) {
    print(letter)
}

Upon loop completion, the loop variable in the example above:

1. will reset to “z”.
2. will disappear.
3. will be “c”.
4. will return to “a”.

Analysis

1. indicates a lack of understanding of program control and variable re-assignment.
2. indicates a confusion between local and global variables, perhaps confusing loops with functions.
3. correct answer.
4. incorrect understanding of iteration over a loop variable.