Interview Questions for R programming

1. How R commands are written?

By using # at the starting of the line of code like #division commands are written.

2. What is t-tests() in R?

It is used to determine that the means of two groups are equal or not by using t.test() function.

3.What are the disadvantages of R Programming?

The disadvantages are:-

• Lack of standard GUI
• Not good for big data.
• Does not provide spreadsheet view of data.

4.What is the use of With () and By () function in R?

with() function applies an expression to a dataset.

#with(data,expression)

By() function applies a function t each level of a factors.

#by(data,factorlist,function)

5. In R programming, how missing values are represented?

In R missing values are represented by NA which should be in capital letters.

6. What is the use of subset() and sample() function in R?

Subset() is used to select the variables and observations and sample() function is used to  generate  a random sample of the size n from a dataset.

7. Explain what is transpose.

Transpose is used for reshaping of the data which is used for analysis. Transpose is performed by t() function.

8. What are the advantages of R?

• The advantages are:-
• It is used for managing and manipulating of data.
• No license restrictions
• Free and open source software.
• Graphical capabilities of R are good.
• Runs on many Operating system and different hardware and also run on 32 & 64 bit processors etc.

Now that you are aware of the benefits of R programming

9. What is the function used for adding datasets in R?

For adding two datasets rbind() function is used but the column of two datasets must be same.

Syntax: rbind(x1,x2……) where x1,x2: vector, matrix, data frames.

10. How you can produce co-relations and covariances?

Cor-relations is produced by cor() and covariances is produced by cov() function.

11.What is difference between matrix and dataframes?

Dataframe can contain different type of data but matrix can contain only similar type of data.

12.What is difference between lapply and sapply?

lapply is used to show the output in the form of list whereas sapply is used to show the output in the form of vector or data frame

13. What is the difference between seq(4) and seq_along(4)?

Seq(4) means vector from 1 to 4 (c(1,2,3,4)) whereas seq_along(4) means a vector of the  length(4) or 1(c(1)).

14. Explain how you can start the R commander GUI.

rcmdr command is used to start the R commander GUI.

15. What is the memory limit of R?

In 32 bit system memory limit is 3Gb but most versions limited to 2Gb and in 64 bit system memory limit is 8Tb.

16.How many data structures R has?

There are 5 data structure in R i.e. vector, matrix, array which are of homogenous type and other two are list and data frame which are heterogeneous.

17. Explain how data is aggregated in R.

There are two methods that is collapsing data by using one or more BY variable and other is aggregate() function in which BY variable should be in list.

18.  Explain how you can start the R commander GUI? 

Typing the command, (“Rcmdr”) into the R console starts the R commander GUI.

19. What are R packages?

Packages are the collections of data, R functions and compiled code in a well-defined format and these packages are stored in library.

20. What is the workspace in R?

Workspace is the current R working environment which includes any user defined objects like vector, lists etc.

21. What is the function which is used for merging of data frames horizontally in R?

Merge()function is used to merge two data frames
Eg. Sum<-merge(data frame1,data frame 2,by=’ID’.

22. what is the function which is used for merging of data frames vertically in R?

rbind() function is used to merge two data frames vertically.
Eg.

Sum<- rbind(data frame1,data frame 2)

23. What is the power analysis?

It is used for experimental design .It is used to determine the effect of given sample size.

24. Which package is used for power analysis in R?

Pwr package is used for power analysis in R.

25. Which method is used for exporting the data in R?

There are many ways to export the data into another formats like SPSS, SAS , Stata , Excel Spreadsheet.

26. Which packages are used for exporting of data?

For excel xlsReadWrite package is used and for sas,spss ,stata foreign package is implemented.

27. How impossible values are represented in R?

In R NaN is used to represent impossible values.

28. Which command is used for storing R object into a file?

Save command is used for storing R objects into a file.
Syntax: >save(z,file=”z.Rdata”)

29. Which command is used for restoring R object from a file?

load command is used for storing R objects from a file.
Syntax: >load(”z.Rdata”)

30. What is the use of coin package in R?

Coin package is used to achieve the re randomization or permutation based statistical tests.

31. Which function is used for sorting in R?

order() function is used to perform the sorting.

32. What is the use of tapply?

IOS-6.1.3

33. What happens when the application object does not handle an event?

The event will be dispatched to your delegate for processing.

34. Explain app specific objects which store the app contents.

The app specific objects are Data model objects that store app’s contents.

35. Explain the purpose of using UIWindow object?

UIWindow object coordinates the one or more views presenting on the screen.

36. Tell me the super class of all view controller objects.

UIView Controller class.

37. How to create axes in the graph?

Using axes() function custom axes are created.

38. What is the use of abline() function?

abline() function is add the reference line to a graph.
Syntax:-

abline(h=yvalues, v=xvalues)

39. Why vcd package is used?

vcd package provides different methods for visualizing multivariate categorical data.

40. What is GGobi?

GGobi is an open source program for visualization for exploring high dimensional typed data.

41. What is iPlots?

It is a package which provide bar plots, mosaic plots, box plots, parallel plots, scatter plots and histograms.

42. What is the use of lattice package?

lattice package is to improve on base R graphics by giving better defaults and it have the ability to easily display multivariate relationships.

43. What is fitdistr() function?

It is used to provide the maximum likelihood fitting of univariate distributions. It is defined under the MASS package.

44. Which data structures are used to perform statistical analysis and create graphs.

Data structures are vectors, arrays, data frames and matrices.

45. What is the use of sink() function?

It defines the direction of output.

46. Why library() function is used?

This function is used to show the packages which are installed.

47. Why search() function is used?

By this function we see that which packages are currently loaded.

48.On which type of data binary operators are worked?

Binary operators are worked on matrices, vectors and scalars.

49. What is the use of doBY package?

It is used to define the desired table using function and model formula.

50. Explain how you can start the R commander GUI?

Typing the command, (“Rcmdr”) into the R console starts the R commander GUI.