Question

Using R Studio:


1)Use the `mtcars` data (`data(mtcars)`) to answer these questions:  
a) Which rows of the data frame contain cars that weigh more than 4000 pounds (the variable is `wt`, units are 1000 pounds).
b) Which cars are these? (*Hint:* since rows are named by car name, use `row.names()`).
c) What is the mean displacement (in inches^3^ ) for cars with at least 200 horsepower (`hp`).
d) Which car has the highest fuel economy (`mpg`)?
e) What was the fuel economy for the Honda Civic?

2) Using the `mtcars` data create a new variable for horespower per unit weight (`hp/wt`). Is this a better predictor of acceleration (`qsec`; seconds to complete a quarter mile) than horsepower alone?

3) Use the function `subset()` to return the cars with 4 cyclinders and automatic transmissions (`am` = `0`). (*Hint:* see `?subset`).

Answer 1

Question 1)

Below is the R code for the given problem. Please follow comments-

R Code-

# Question 1
# a)
# filtering cars with wt more than 4
filter(mtcars, wt > 4.0)

# b)
# List of cars with wt more than 4
mtcars[ which(mtcars$wt>4 ), ]

# c)
# Finding mean disp of cars with hp greater than 200
mtcars %>%
filter(hp > 200) %>%
summarise(mean = mean(disp))

# d)
# Using max function to find cars with maximum mpg
mtcars[ which(mtcars$mpg== max(mtcars$mpg)),]
# e)
# Fuel economy of honda civic
mtcars[grep('^Honda', rownames(mtcars)),]

Code screenshot-

Output-