3 Data Structure in R

Data Structure in R

1. Dr Nisha Arora
Data Structure in R
https://www.linkedin.com/in/drnishaarora/

2. Contents
2
Data Structure in R
Vector
List
Factor
Matrix
Data Frame
Array
Subsetting & Basic Operations

3. 3
Coercion
Allelementsofavectormustbethesametype,sowhenwe
attempttocombinedifferenttypestheywillbecoercedtothe
mostflexibletype.
Typesfromleasttomostflexibleare:
.
Logical
Integer
Double/ Numeric
Character

4. 4
Coercion
Whenalogicalvectoriscoercedtoanintegerordouble,TRUE
becomes1andFALSEbecomes0
x<-c(FALSE,FALSE,TRUE);as.numeric(x)
TotalnumberofTRUEs
sum(x)
ProportionthatareTRUE
mean(x)

5. 5
Coercion in R
✓Toforcefullycoerceavariableclassintoother,following
functionsareused
as.numeric(),as.logical(),etc.
In Python, we call it ‘typecasting’
https://youtu.be/FJ6IkFycCdA

6. 6
Data Structure in R
✓Vector
ThebasiconedimensionaldatastructureinRisthevector
✓List
Listsaregenericvectorswhichcancontainanydatatypeor
datastructure
✓Matrix
ThebasictwodimensionaldatastructureinRisthematrix
Note:Avariablewithasinglevalueisknownasscalar.InRa
scalarisavectoroflength1

7. 7
Data Structure in R
✓Factor
Afactorisavectorthatcancontainonlypredefinedvalues,and
isusedtostorecategoricaldata
✓DataFrame
Adataframeisalistofequal-lengthvectors.Thismakesita2-
dimensionalstructure,soitsharespropertiesofboththematrix
andthelist.
✓Array
Anarrayisann-dimensionaldatastructure.Matrixisanspecial
caseofarrayfor2dimensions.
We will discuss ‘tibble’ from tidyversein next lession

8. 8
Vectors in R
TocreatevectorsinRusingconcatenationfunction
num_var<-c(1,2,4.5)
UsetheLsuffixtogetanintegerratherthanadouble
int_var<-c(13L,0L,10L)
UseTRUEandFALSE(orTandF)tocreatelogicalvectors
log_var<-c(TRUE,FALSE,T,F)
Usedoubleorsinglequotationtocreatecharactervector
chr_var<-c(“abc",“123")
Vectorscanalsobecreatedbyusingsequenceorscanfunction

9. 9
Vectors in R
Tonameavector
#Assigningnamesdirectly
x<-c(Mon=37,Tue=41.4,Wed=43.2)
#Usingnames()function
x<-c(78,86,89);names(x)<-c(“chem",“phy",“math")
#UsingsetNames()function
x<-setNames(1:3,c("a","b","c"))

10. 10
Vector Subsetting
x=c(11,42,23,14,55);
names(x)=c('ajay','ravi','john','anjali','namrata');x
x[2];x[1:3];x[5];x[7]
#x[n]gives'nth'elementofvectorx,thereareonly6elements,
sox[7]isNA
x['ajay'];x[c('ravi','namrata’)]
#Toselectelementsbynames

11. 11
List in R
Listsaredifferentfromvectorsbecausetheirelementscanbeof
anytype,includinglists.
Wecanconstructlistsbyusinglist()insteadofc()
x<-list(1:4,"abc",c(T,T,F),c(2.3,5.9))

12. 12
List Subsetting
https://stackoverflow.com/a/49699955/5114585
Threeways:
Usingsinglesquare
bracket‘[]’
UsingDoublesquare
bracket‘[[]]’
Calling‘$’byusing
names

13. 13
Matrix in R
TocreatematrixinR
x=matrix(1:9,nrow=3,ncol=3)
x=matrix(1:9,3,3)#Alternateway
Tocreateamatrixbyusingbyrow
z=matrix(1:9,nrow=3,ncol=3,byrow=TRUE)
#BydefaultbyrowisFALSE,somatrixiscreatedbycolumn
a<-matrix(1:9,byrow=TRUE,nrow=3)#Alternateway

14. 14
Matrix in R
Tocreatematrixbyusingcbind()command
one<-c(1,0,0)
two<-c(0,1,0)
three<-c(0,0,1)
b<-cbind(one,two,three)
Tocreateamatrixbyusingrbind()command
c<-rbind(one,two,three)

15. 15
Matrix in R
Toassignnamestocolumnsandrowsofmatrix
x=cbind(c(78,85,95),c(99,91,85),c(67,62,63))
colnames(x)=c(“Jan",‘Feb',“Mar“)
rownames(x)=c(“product1”,‘product2’,‘product3’)
Otherusefulcommands
dim(x);head(x);nrow(x);ncol(x);attributes(x)
rowSums(x);colSums(x)

16. 16
Matrix Subsetting
Tofindsubmatricesofagivenmatrix
x<-matrix(1:6,2,3)
x[1,2]#Elementoffirstrow,secondcolumn[singleelement]
x[2,1]#Elementofsecondrow,firstcolumn[singleelement]
x[2,]#Matrixofalltheelementsofsecondrow[matrix]
x[,1]#Matrixofalltheelementsoffirstcolumn[matrix]
x[1:2,3]#Elementsoffirst&secondrowforthirdcolumnonly

17. 17
Matrix Subsetting
Tofindsubmatricesofagivenmatrix
x<-matrix(1:6,2,3)
Bydefault,whenasingleelementofamatrixisretrieved,itisreturned
asavectoroflength1ratherthana1×1matrix.
Thisbehaviourcanbeturnedoffbysettingdrop=FALSE.
x[1,2] #Singleelement
x[1,2,drop=FALSE] #Matrixofonerow&onecolumn

18. 18
Matrix Subsetting
Tofindsubmatricesofagivenmatrix
x<-matrix(1:6,2,3)
Similarly,sub-settingasinglecolumnorasinglerowresultsina
vector,notamatrix(bydefault).
Thisbehaviourcanbeturnedoffbysettingdrop=FALSE.
x[1,] #Singlerow
x[1,,drop=FALSE] #Matrixofonerow&onecolumn

19. 19
Matrix Subsetting
Tofindsubmatricesofagivenmatrix
x=cbind(c(78,85,95),c(99,91,85),c(67,62,63))
x[,2]
x[,2:3]
x[2,3]
x[1:2,3]

20. 20
Factors in R
They are used for handling categorical variable, e.g., the ones
that are nominal or ordered categorical variables.
For example,
Male, Female Nominal categorical
Low, Medium, High Ordinal categorical

21. 21
Factors in R
To create a factor in R using factor()
gender_vector <-c("Male", "Female", "Female", "Male", "Male")
factor_gender_vector <-factor(gender_vector)
Also, try levels(factor_gender_vector)
To change the levels of factor
levels(factor_gender_vector) = c(("F", "M"))
Other useful commands
summary(factor_gender_vector); table(factor_gender_vector)

22. 22
Data frames in R
AdataframeisthemostcommonwayofstoringdatainR,andifused
systematicallymakesdataanalysiseasier.
✓Similartotables(databases),dataset(Excel/SAS/SPSS)etc.
✓Consistsofcolumnsofdifferenttypes;Moregeneralthanamatrix
✓Columns–Variables;Rows–Observations
✓Convenienttoholdallthedatarequiredforadataanalysis
✓Theyarerepresentedasaspecialtypeoflistwhereeveryelementof
thelisthastohavethesamelength
✓Dataframesalsohaveaspecialattributecalledrow.names

23. 23
Data frames in R
✓Dataframesare,well,tables(likeinanyspreadsheetprogram).
✓Indataframesvariablesaretypicallyinthecolumns,andcasesin
therows.
✓Columnscanhavemixedtypesofdata;somecancontain
numeric,yetotherstext.
✓Ifallcolumnswouldcontainonlycharacterornumericaldata,
thenthedatacanalsobesavedinamatrix(thosearefasterto
operateon).
We will also discuss ‘tibble’ in the course.

24. 24
Data frames in R
TocreateadataframeinR
Example_1:
df<-data.frame(x=1:3,y=c("a","b","c"))
Example_2:
height<-c(180,175,190)
weight<-c(75,82,88)
name<-c("Anil","Ankit","Sunil")
data<-data.frame(name,heigth,weight)

25. 25
Data frames in R
TocombinedataframesinR
Example_1:usingcbind()
df<-data.frame(x=1:3,y=c("a","b","c"))
cbind(df,data.frame(z=3:1))
Example_2:usingrbind()
rbind(df,data.frame(x=10,y="z"))

26. 26
Data frames in R
TocombinedataframesinR
Example_1:usingcbind()
df<-data.frame(x=1:3,y=c("a","b","c"))
cbind(df,data.frame(z=3:1))
Example_2:usingrbind()
rbind(df,data.frame(x=10,y="z"))

27. 27
Data Type Conversions
Useis.foototestfordatatypefoo.
ReturnsTRUEorFALSE
Useas.footoexplicitlyconvertit.
Examples:
is.numeric(),is.character(),is.vector(),is.matrix(),is.data.frame()
as.numeric(),as.character(),as.vector(),as.matrix(),as.data.frame)

28. 28
Handling of missing values
X<-c(1:8,NA)
✓Removingmissingvlaues
mean(X,na.rm=T)ormean(X,na.rm=TRUE)
✓Tocheckforthelocationofmissingvalueswithinavector
which(is.na(X))
✓Toassignthisalargenumber,say,999
X[which(is.na(X))]=999
For more code: follow me on GitHub

29. 29
Handling of missing values
x<-c(1,2,NA,4,NA,5)
✓Identifymissingvalues
bad<-is.na(x)
✓Toremovemissingvalues
x[!bad]

30. 30
Handling of missing values
x<-c(1,2,NA,4,NA,5);y<-c("a","b",NA,"d","e",NA)
df=data.frame(x,y)
✓Totakethesubsetofdataframewithnomissingvalue
good=complete.cases(x,y);good
✓Totakethesubsetofvectorxwithnomissingvalue
x[good]
✓Totakethesubsetofvectorywithnomissingvalue
y[good]

31. Books
31
✓ Crowley,M.J.(2007).TheRBook.Chichester,New
England:JohnWiley&Sons,Ltd.
✓ AnIntroductiontoRbyW.N.Venables,D.M.Smithand
theRCoreTeam
✓ RinaNutshellbyJosephAdler:O’Reilly
✓ Teetor,P.(2011).Rcookbook.Sebastopol,CA:O’Reilly
MediaInc.

32. Books
32
✓BioStatistics-https://www.middleprofessor.com/files/applied-
biostatistics_bookdown/_book/
✓AdvancedR-https://adv-r.hadley.nz/
✓DataVisualization-https://rkabacoff.github.io/datavis/
✓RforDataScience-https://r4ds.had.co.nz/index.html
✓Data Exploration & Analysis -
https://bookdown.org/mikemahoney218/IDEAR/
✓https://bookdown.org/mikemahoney218/LectureBook/

33. Blogs & Communities
33
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

34. Learn To Code
34
https://www.datacamp.com/
https://www.dataquest.io/
https://www.codeschool.com/
https://guide.freecodecamp.org/r/
https://www.hackerrank.com/contests/co/
https://www.hackerearth.com/practice/
https://hackernoon.com/tagged/r
https://rpubs.com/

35. 35
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
https://github.com/arora123/
https://www.youtube.com/channel/UCniyhvrD_8AM2jXki3eEErw
https://www.linkedin.com/in/drnishaarora/
[email protected]

36. Thank You