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R Programing Interview Questions
To evaluate the association between two or more variables we use Correlation. It has Correlation coefficients which are indicators of the strength of the linear relationship between two different variables say x and y. The correlation coefficient greater than zero indicates that a positive relationship, while a value less than zero indicates that a negative relationship. A negative correlation is also called inverse correlation which is a key concept in the creation of diversified portfolios that can better withstand portfolio volatility. 
The most common Correlation coefficient is generated by the Pearson product-moment correlation which is used to measure the linear relationship between two variables. The Pearson Correlation is also called parametric correlation. 
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)).
There are 5 types of sorting algorithms are used which are :
* Bubble Sort
* Selection Sort
* Merge Sort
* Quick Sort
* Bucket Sort
There are many ways to export the data into another formats like SPSS, SAS , Stata , Excel Spreadsheet.
Save command is used for storing R objects into a file.
Syntax : >save(z,file=”z.Rdata”)
load command is used for storing R objects from a file.
Syntax : >load(”z.Rdata”)
UIWindow object coordinates the one or more views presenting on the screen.
Some packages used for data mining in R :
data.table - provides fast reading of large files

rpart and caret -
for machine learning models.

Arules -
for associaltion rule learning.

GGplot -
provides varios data visualization plots.

tm -
to perform text mining.

Forecast -
provides functions for time series analysis
The cluster.stats() function define in the fpc package that provides a method for comparing the similarity of two cluster solutions using different validation criteria, and the pvclust() function is defined in the pvclust package that provides p-values for hierarchical clustering.
This function defines in the mvnormtest package and produces the Shapiro-wilk test to multivariate normality. The barlett.test() is used to provide a parametric k-sample test of the equality of variances.