Suppose $1,2,3$ stands for KFC$,$ Subway and McDonald respectively. Use factor$()$ to turn the numeric

vector c$(2,1,2,1,3,3)$ into a factor vector named food.

b$)$ Now confirm that food is indeed a factor using str$(),$ which reveals the structure of an R object.

c$)$ Now please change the first element in food from $2$ to $3$

$$ Hint: food$[6]$ will gives the $6$th element in food.

d$)$ Function levels$()$ can produce the labels of the factors. Please correct the all the errors in the code

below, which tries to change the labels into McDonald, Subway and KFC$.$

level$($food$)=$ c$($KFC$,$ Subway, McDonald$)$

e$)$ After fixing the codes in the previous sub$-$question, please use summary$()$ or table$()$ to check the

frequency of McDonald, KFC$,$ and Subway in food.

f$)$ Use plot$()$ to obtain a bar chart of the variable food. Why do you think the bars are sorted on the

x$-$axis this way?

g$)$ There are many ways to re$-$order the levels in a factor but here we will focus on the following two

options here.

$$ relevel$()$ to specify the reference level, i$.$e the category that is first on the list. This has a

particular implication in a regression setting.

$$ Use the levels argument in factor$()$