Data Handling with R MCQ's

1. Which function can be used when a vector needs to be split into groups defined by a classifying factor, compute a function on the subsets, and return the results?

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   tapply

2. Which function is very similar to lapply?

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   sapply

3. Applying lapply function on a matrix returns

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   list

4. A hospital data contains patient's age and treatment they are undergoing. Which function can be used to find average of patients undergoing each of the treatments?

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   tapply

5. Which function is used over the margins of an array

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   apply

6. What will the following lines of code return
x <- matrix(1:18, 6, 3)
apply(x, 2, sum)

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   vector of 3 elements

7. For a given matrix mat, how do you increment every element of the matrix by 3 and return a vector.
(I) sapply(mat, function(x,y) sum(x)+y,y=3)
(II) sapply(mat, function(x) sum(x)+3)

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   I & II

8. The function read.csv() imports data into

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   data frame

9. Which package is used to import data from a SQL server to R?

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   RODBC

10. The function write.csv() exports data into a file. However, this function by default adds rownames to the file. Which argument can be used to turn off addition of rownames?

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   rownames=F

11. nrows and skip arguments in the read.table() command can be used to get

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   All the options

12. Which command can be used to import text files in R

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   read.table()

13. tbl is an extension of:

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   data frame

14. dplyr is useful for:

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   All options

15. Which of the following functions can be used to find the number or rows and columns in a dataset?

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   dim

16. Which of the following functions does not list the total number of observations in a dataset?

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   head

17. Which of the following functions lists all columns in a dataset with few values from each column?

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   glimpse

18. In the hflights dataset, how many flights were cancelled in the month of January 2011

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   209

19. What is the average mileage of a car in the mtcars dataset

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   20....

20. In the iris dataset, how many flowers of species setosa havePetal.Length/Petal.Width ratio of less than 10.

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   45

21. In the iris dataset, how many flowers havePetal.Length/Petal.Width ratio of less than 10

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   145

22. In the mtcars dataset, how many cars provide a mileage of less than 20 mpg?

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   18

23. dplyr never prints row names since no dplyr method is guaranteed to preserve them.

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   True

24. If x and y are two tbls, which of the following joins return all rows from x and y irrespective of matching values?

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   full join

25. If x and y are two tbls, which of the following joins return all rows from x where there are matching values in y, and all columns from x and y

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   inner join

26. If x and y are two tbls, which of the following joins return all rows from x where there are not matching values in y, keeping just columns from x?

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   anti-join

27. Join functions return results of data type

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   data frame

28. If x and y are two tbls, which of the following joins return all rows from y, and all columns from x and y?

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   right join

29. If x and y are two tbls, which of the following joins return all rows from x where there are matching values in y, keeping just columns from x?

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   semi join

30. Data table is mainly used for aggregation

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   False

31. Which of the following is multivariate version of lapply?

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   lapply