This set of tricky R Programming questions and answers focuses on “Commands”.

1. Which of the following code will drop the nth column ?

a) new <- old[-n,].

b) new <- old[,-n].

c) new <- old[,-c(i,j)].

d) new <- subset(old,logical)

View Answer

Explanation: new <- old[-n,] drops the nth row.

2. Which of the following code drop the ith and jth column ?

a) new <- old[-n,].

b) new <- old[,-n].

c) new <- old[,-c(i,j)].

d) new <- subset(old,logical)

View Answer

Explanation: new <- subset(old,logical) select those cases that meet the logical condition.

3. Which of the following statement find cases with no missing values ?

a) complete <- subset(data.df,complete.cases(data.df)

b) complete <- sub(data.df,complete.cases(data.df)

c) complete <- subset(data.df,completeall.cases(data.df)

d) new <- old[n1:n2,n3:n4].

View Answer

Explanation: new <- old[n1:n2,n3:n4] select the n1 through n2 rows of variables n3 through n4.

4. Which of the following statement is normal distribution ?

a) dnorm(x, mean=0, sd=1, log = FALSE)

b) pnorm(q, mean=0, sd=1, lower.tail = TRUE, log.p = FALSE)

c) qnorm(p, mean=0, sd=1, lower.tail = TRUE, log.p = FALSE)

d) rnorm(n, mean=0, sd=1)

View Answer

Explanation: d stands for density.

5. which of the following statement gives cumulative sum ?

a) cumsum(x,na=rm=TRUE)

b) cumprod(x)

c) cummax(x)

d) cummin(x)

View Answer

Explanation: cummax() function returns the cumulative maxima.

6. Which of the following is uniform distribution ?

a) dunif(x, min=0, max=1, log = FALSE)

b) punif(q, min=0, max=1, lower.tail = TRUE, log.p = FALSE)

c) qunif(p, min=0, max=1, lower.tail = TRUE, log.p = FALSE)

d) runif(n, min=0, max=1)

View Answer

Explanation: These functions provide information about the uniform distribution on the interval from min to max.

7. Which of the following truncates real x to integers ?

a) as.order(x)

b) as.integer(x)

c) as.numeric(x)

d) as.character(x)

View Answer

Explanation: as.integer for object of class truncates decimal part of image values and then converts to type integer.

8. Which of the following tests each element of x for membership in y?

a) y%in%x

b) all(x)

c) any(x)

d) x%in%y

View Answer

Explanation: y%in%x tests each element of y for membership in x. x%in%y tests each element of x for membership in y.

9. Which of the following finds the maximum value in the vector x, exclude missing values

a) rm(x)

b) max(x, na.rm=TRUE)

c) all(x)

d) x%in%y

View Answer

Explanation: all(x%in%y) returns true if x is a proper subset of y.

10. Which of the following produces the variance covariance matrix ?

a) sd(x, na.rm=TRUE)

b) mad(x, na.rm=TRUE)

c) fivenum(x, na.rm=TRUE)

d) var(x, na.rm=TRUE)

View Answer

Explanation: mad(x, na.rm=TRUE) gives median absolute deviation.var(y) instructs R to calculate the sample variance of Y. In other words it uses n-1 ‘degrees of freedom’, where n is the number of observations in Y.sd(y) instructs R to return the sample standard deviation of y, using n-1 degrees of freedom.

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