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d.pizza is a data frame. Its column named temperature contains only numbers. If you extract temperature using the [] accessors, its class defaults to numeric. How can you access temperature so that it retains the class of data.frame?

> class( d.pizza[ , "temperature" ] )

>"numeric"

• class( d.pizza[ , "temperature" ] )
• class( d.pizza[ , "temperature", drop=F ] )
• class( d.pizza$temperature )
• class( d.pizza( , "temperature") )

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You accidentally display a large data frame in the R console, losing all the statements you entered during the current session. What is the best way to get the prior 25 statements back?

• history()
• history(max.show = 25)
• console(-25)
• console(reverse=TRUE)

Linkedin R assessment Quiz answers

What does c contain?

a <- c(3, 3, 6.5, 8)

b <- c(7, 2 ,5.5, 10)

c <- a < b

• [1] TRUE FALSE FALSE TRUE
• [1] -4
• [1] NaN
• [1] 4 -1 -1 2

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Review the statements below. Does the use of the dim function change the class of y, and if so what is y's new class?

> y <- 1:9

> dim(y) <- c(3,3)

• No, y's new class is "array."
• No, y's new class is "vector."
• Yes, y's new class is "integer."
• Yes, y's new class is "matrix."

Linkedin R assessment questions

What is mydf$y in this code? 

mydf <- data.frame(x = 1:3, y = c("a", "b", "c"), stringsAsFactors = FALSE)

• list
• string
• character vector
• factor

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