Data Handling using R | Fresco Play

Question 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?

Answer: tapply

Question 2: Which function is very similar to lapply?

Answer: sapply

Question 3: Applying lapply function on a matrix returns

Answer: list

Question 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?

Answer: tapply

Question 5: Which function is used over the margins of an array

Answer: apply

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

Answer: vector of 3 elements

Question 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)

Answer: I & II

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

Answer: data frame

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

Answer: RODBC

Question 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?

Answer: rownames=F

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

Answer: All the options

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

Answer: read.table()

Question 13: tbl is an extension of:

Answer: data frame

Question 14: dplyr is useful for:

Answer: All the options mentioned

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

Answer: dim

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

Answer: head

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

Answer: glimpse

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

Answer: 209

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

Answer: 20....

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

Answer: 45

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

Answer: 145

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

Answer: 18

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

Answer: True

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

Answer: full_join

Question 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

Answer: inner join

Question 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?

Answer: anti_join

Question 27: Join functions return results of data type

Answer: data frame

Question 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?

Answer: right_join

Question 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?

Answer: semi_join

Question 30: Data table is mainly used for aggregation

Answer: False

Question 31: Which of the following is multivariate version of lapply?

Answer: 1. lapply 2. apply

Question 32: Which of the following methods can be used to add a new column to a dataframe?

Answer: All the options mentioned

Question 33: Which of the following data structures in R can store different types of data?

Answer: List, Data Frame

Question 34: Which function do you use to print the names of all columns in a data frame?

Answer: names()

Question 35: Which of the following command's print a subset of the dataset mtcars?

Answer: All the options mentioned

Question 36: How to find structure of a dataframe

Answer: struct()

Question 37: Which of the following is not correct?

Answer: Data frames do not support variables of different type

Question 38: How to find structure of a dataframe

Answer: str()

Question 39: Which of the following functions can be used to create a data frame in R?

Answer: data.frame()

Question 40: What is the average horsepower of 4 gear, automatic transmission cars in the R built-in dataset "mtcars"

Answer: 83.875

Question 41: What is the average mileage(mpg) of 6 cylinder, manual transmission cars in the R built-in dataset "mtcars"

Answer: 20.56667

Question 42: What is SQL equivalent of "i" in a typical data table query

Answer: WHERE

Question 43: By default R stores strings in data frames as:

Answer: factor

Question 44: Which of the following command's will print the dataset "mtcars" tin ascending order of their mileage?

Answer: mtcars[rev(order(mtcars$mpg)),]

Question 45: Set operation that returns all observations from two tbls x and y, without removing duplicates.

Answer: union_all()