What is the principal difference between an array and a matrix?

Which is not a property of lists and vectors?

Which function displays the first five rows of the data frame named pizza?

You accidentally display a large data frame on 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?

What is mydf$y in this code? mydf <- data.frame(x=1:3, y=c("a","b","c"), stringAsFactors=FALSE)

How does a vector differ from a list?

Suppose we define X <- NA. What is the output for > is.nan( X ); is.na( X )

What is the output of this command: > is.na( c( 1:3, NA ) )

Which R function adds a line with slope 1 and intercept 0 into an existing plot of Y versus X?

What's the output for command: seq(from = 1, to = 5, by = 3)

What is the output of the following R code? x<-2; y <- c(1:3); paste("The value of x is", x, "and the value of y[x] is", y[x], sep=" ")