Quiz 3

Which of the following statements are TRUE about unique() function?

• unique() removes duplicates based on all the columns in the argument.
• Usage of unique() should be avoided as far as possible.
• Both of the above are true.
• None of the above

Which of the following line of code will always extract exactly one element stored in dat?

• dat[1, 2]
• unique( dat )
• unique( dat[ ,2] )
• dat[1:3, ]
• None of the above

Which R code is used to permanently change the dataset dat?

• unique( dat[, 2] )
• order( dat )
• head( dat )
• dat[1, 2] <- 5
• None of the above

Assuming dat has 100 observations and five variables, which R code would have the effect of changing the original data from the dataset dat?

• dat[1, 2] <- NA
• dat[ !is.na(dat[ , 1]), 1] <- NA
• Both of the above are true.
• None of the above

Assuming dat has 100 observations and five variables, with R code, how do you select the third column from the dataset named dat?

• dat[ , 3]
• dat[1, 3]
• dat[3, ]
• dat[3, 1]
• None of the above

Assuming dat has 100 observations and five variables, which R code would output only two columns from a dataset named dat?

• dat[1:2, ]
• dat[, 1:2]
• Both of the above are true.
• dat[ c(1, 2), ]
• None of the above

With R, how do you output all the observations from a dataset named dat where the values of the second column is greater than 3?

• dat[ , 2] > 3
• dat[2, ] > 3
• dat[ dat[ , 2] > 3, ]
• None of the above

The logical operator "|" displays an entry if ANY conditions listed are TRUE. The logical operator "&" displays an entry if ALL of the conditions listed are TRUE

• True
• False

Which R code would be used to sort all the elements of the first column of the dataset dat?

• order( dat[ , 1] )
• order( dat$1 )
• dat[ order, 1 ]
• dat[ order(), 1]
• None of the above

With R, how can you replace the entries where the value is 3 with NA in a dataset named dat?

• dat[ dat == 3 ] <- NA
• dat[ is.na(), 3]
• is.na( dat == 3 )
• dat <- 3