Dr Nisha Arora

Descriptive Statistics with R

Contents

2

Tabulation & Cross Tabulation

Built-in Functions for Descriptive Statistics

Built-in Functions for Probability Distribution

References

3

Frequency Tables

To create a one-dimensional frequency table

Load & understand data

data = iris; names(data); help(iris)

Create frequency table for variable ‘Species’ of ‘iris’ data set

table(iris$Species)

4

Cross Tabulation

To create a two-dimensional contingency table

Load & understand data

data = iris; names(data); help(iris)

Create frequency table of sepal length of different species of

‘iris’ data set

table(iris$Sepal.Length, iris$Species)

Example_2:

mtcars; table(mtcars$cyl, mtcars$gear)

5

Cross Tabulation

To create a two-dimensional contingency table

Load & understand data

read.csv("people2.csv"); names(people2)

Create frequency table of eye color of people categorized by

sex

table2 <- table(people2$Eye.Color, people2$Sex)

6

Cross Tabulation

Table of proportions

prop.table(table2)

# table with each cell count expressed as a proportion of the

total count

prop.table(table2, margin=1)

# table with each cell count expressed as a proportion of row

total

prop.table(table2, margin=2) # table with each cell count

expressed as a proportion of column total

Table of percentages

round(prop.table(table2)*100)

7

Cross Tabulation

Table with marginal sums

add.margins(table2)

# table with row and column totals

addmargins(table2, margin=1)

# table with row total

addmargins(table2, margin= 2)

# table with column total

To perform chi-square test of association

summary(table2)

8

Cross Tabulation

To create a three-dimensional contingency table

Load & understand data

people2 <- read.csv("people2.csv"); names(people2)

Create frequency table of eye color of people categorized by

their sex & height

table(people2$Eye.Color, people2$Sex, people2$Height.Cat)

Built-in functions for Descriptive Statistics

9

Statistics Function name/command

Mean mean

Median median

Standard Deviation sd

Median Absolute Deviation mad

Variance var

Maximum Value max

Minimum Value min

Range range

Interquartile range IQR

Built-in functions for Descriptive Statistics

10

Statistics Function name/command

Quantiles quantile

Tukey’s five-number

summary

[min, I, II, III quartile, max

value]

fivenum

Sum sum

Product prod

Number of observations length

Standardize/ Computing

z-score

scale(x, center=TRUE, scale=TRUE)

Mean Centering scale(x, scale=FALSE)

Built-in functions for Probability Distribution

11

Statistics Function name/command

Normal PDF dnorm

Cumulative Normal

Probability pnorm

Normal Quantile qnorm

Random Normal Variable rnorm

Similarly, there are functions for other distributions like rbinom,

rpois, rt, runif, rf etc.

12 Source: Google Images

References

13

• Crowley, M. J. (2007). The R Book. Chichester, New

England: John Wiley & Sons, Ltd.

• An Introduction to R by W. N. Venables, D. M. Smith

and the R Core Team

• R in a Nutshell by Joseph Adler: O’Reilly

• Teetor, P. (2011). R cookbook. Sebastopol, CA:

O’Reilly Media Inc.

References

14

http://www.r-bloggers.com/

http://www.inside-r.org/blogs

https://blog.rstudio.org/

http://www.statmethods.net/

http://stats.stackexchange.com

https://www.researchgate.net

https://www.quora.com

https://github.com

References

15

https://rpubs.com/

https://www.datacamp.com/

https://www.dataquest.io/

https://www.codeschool.com/

16

Reach Out to Me

http://stats.stackexchange.com/users/79100/learner

https://www.researchgate.net/profile/Nisha_Arora2/contributions

https://www.quora.com/profile/Nisha-Arora-9

nishaarora4@gmail.com

Thank You