Key for Computing Assignment 1

r-assign-01-key.R

# Computing Assignment 1 Code

### Question 1

x <- c(3, 4, 2, 6, 1)  # create a numeric vector

### Question 2

3*x  # multiply the numeric vector by three

### Question 3

sum(x)  # sum all the elements in the numeric vector

### Question 4

# step 1
y <- c("R", "R", "D", "D", "I", "R")  # create character vector
table(y)  # print a table of the character vector
print(y)  # print the character vector itself

# step 2
z <- factor(y, levels = c("R", "I", "D"))  # create factor by adding levels 
table(z)  # print a table of the factor vector
print(z)  # print the factor vector itself

### Question 5

# step 1
m <- c(3, 2, 1, NA)  # create a numeric vector with a missing value

# step 2: try and fail
mean(m) # find the average; returns NA
# This function returns NA (missing value) because the vector contains a missing
# value. If one or more values are not know (i.e., missing), then the mean
# itself is not known (i.e., missing) because the mean requires us to know the
# sum of all the elements.

# step 3: try and succeed
mean(m, na.rm = TRUE) # find the average; returns a number
# This function returns a number by dropping the missing observation and
# calcuating the mean as the sum of the non-missing observations divided by the
# number of non-missing observations. In this exmaple, it's (3 + 2 + 1)/3 = 2.