R Programming Questions and Answers – Vectorized Operations-2

This set of R Programming Interview Questions and Answers for experienced focuses on “Vectorized Operations”

1. Which of the following function gives the day of the week ?
a) weekdays
b) months
c) quarters
d) all of the mentioned
View Answer

2. Point out the correct statement :
a) Times use the POSIXct and POSIXlt class
b) Dates and times have special classes in R that allow for numerical and statistical calculations
c) Character strings can be coerced to Date/Time classes using the strptime function
d) All of the mentioned
View Answer

3. What would be the output of the following code ?

> p <- as.POSIXlt(x)
> names(unclass(p))
> p$wday

a) 1
b) 2
c) 3
d) NULL
View Answer

4. What would be the output of the following code ?

> datestring <- c("January 10, 2012 10:40", "December 9, 2011 9:10")
> x <- strptime(datestring, "%B %d, %Y %H:%M")
> x

a) “2012-01-10 10:40:00 EST” “2011-12-09 09:10:00 EST”
b) “2012-01-10 10:40:00 IST” “2011-12-09 09:10:00 IST”
c) “2012-01-10 10:40:00 GMT” “2011-12-09 09:10:00 GMT”
d) All of the mentioned
View Answer

5. Point out the wrong statement :
a) POSIXct is just a very large integer under the hood
b) POSIXlt stores a bunch of other useful information like the day of the week, day of the year, month, day of the month
c) There are a number of generic functions that work on dates and times to help you extract pieces of dates and/or times
d) None of the mentioned
View Answer

6. What would be the output of the following code ?

> x <- as.Date("2012-01-01")
> y <- strptime("9 Jan 2011 11:34:21", "%d %b %Y %H:%M:%S")
> x-y

a) Time difference of 356.3095 days
b) Warning
c) NULL
d) All of the mentioned
View Answer

7. What would be the output of the following code ?

> x <- as.Date("2012-03-01")
> y <- as.Date("2012-02-28")
> x-y

a) Time difference of 3 days
b) Time difference of 2 days
c) Time difference of 1 days
d) All of the mentioned
View Answer

8. Which of the followin code represents internal representation of a Date object ?
a) class(as.Date(“1970-01-02”))
b) unclass(as.Date(“1970-01-02”))
c) unclassint(as.Date(“1970-01-02”))
d) all of the mentioned
View Answer

9. What would be the output of the following code ?

> x <- as.POSIXct("2012-10-25 01:00:00")
> y <- as.POSIXct("2012-10-25 06:00:00", tz = "GMT")
> y-x

a) Time difference of 1 hour
b) Time difference of 1 min
c) Time difference of 1 sec
d) None of the mentioned
View Answer

10.What would be the output of the following code ?

> x <- matrix(1:4, 2, 2)
> y <- matrix(rep(10, 4), 2, 2)
> x %*% y

a)

[,1] [,2]
[1,] 40 40
[2,] 60 60

b)

[,1] [,2]
[1,] 40 40
[2,] 80 60

c)

[,1] [,2]
[1,] 40 60
[2,] 60 60

d) None of the mentioned
View Answer

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