Chapter 6 Vector functions

In this chapter, we’ll cover the core functions for vector objects. The code below uses the functions you’ll learn to calculate summary statistics from two exams.

# 10 students from two different classes took two exams.
#  Here are three vectors showing the data
midterm <- c(62, 68, 75, 79, 55, 62, 89, 76, 45, 67)
final <- c(78, 72, 97, 82, 60, 83, 92, 73, 50, 88)

# How many students are there?
length(midterm)
## [1] 10

# Add 5 to each midterm score (extra credit!)
midterm <- midterm + 5
midterm
##  [1] 67 73 80 84 60 67 94 81 50 72

# Difference between final and midterm scores
final - midterm
##  [1] 11 -1 17 -2  0 16 -2 -8  0 16

# Each student's average score
(midterm + final) / 2
##  [1] 72.5 72.5 88.5 83.0 60.0 75.0 93.0 77.0 50.0 80.0

# Mean midterm grade
mean(midterm)
## [1] 72.8

# Standard deviation of midterm grades
sd(midterm)
## [1] 12.67368

# Highest final grade
max(final)
## [1] 97

# z-scores
midterm.z <- (midterm - mean(midterm)) / sd(midterm)
final.z <- (final - mean(final)) / sd(final)