**81. Mention how you can produce co-relations and covariances?**

You can produce co-relations by the cor () function to produce co-relations and cov () function to produce covariances.

**82. How can you save your data in R?**

To save data in R, there are many ways, but the easiest way of doing this is

Go to Data > Active Data Set > Export Active DataSet and a dialogue box will appear, when you click ok the dialogue box let you save your data in the usual way.

**83. In R how missing values are represented?**

In R missing values are represented by NA (Not Available), why impossible values are represented by the symbol NaN (not a number).

**84. What is data import in R language?**

The user can import data in R language. R commander GUI is used to type the commands, also known as Rcmdr, which is like a console.

**85.Why the function anova(), cv.Im(), stepAIC()?**

**We can use the above functions for the following tasks:**

**Anova()**: Function is used to compare the nested models**lm()**: The function is defined under the DAAG package and is used fork-fold validation**stepAIC()**: The function is defined by the MASS package and can perform stepwise model selection under exact AIC.

**86. Which data structure is used to store categorical variables?**

R has a special data structure called **“factor”** to store categorical variables. It tells R that a variable is nominal or ordinal by making it a factor.

*gender = c(1,2,1,2,1,2)
gender = factor(gender)
gender*

*87. How to rename a variable?*

* **In the example below, we are renaming variable var1 to variable1.*

*df = data.frame(var1=c(1:5))*

*colnames(df)[colnames(df) == ‘var1’] <- ‘variable1’*

*The rename() function in dplyr package can also be used to rename a variable.*

*library(dplyr)*

*df= rename(df, variable1=var1)*

**88. How to remove all the objects**

rm(list=ls())

**89. How R handles missing values?**

Missing values are represented by capital NA.

To create a new data without any missing value, you can use the code below :

*df <- na.omit(mydata)*

### 90. What are various ways to write la oop in R

There are primarily three ways to write a loop in R

- For Loop
- While Loop
- Apply Family of Functions such as Apply, Lapply, Sapply etc