04a Functions for NAs Strings Etc

8/19/2019 04a Functions for NAs Strings Etc

1/17

Data Analysis & DataScience with R

Functions for dealing with NAs,NULLs, dates, strings, regular

expressions, etc.

y !arin Fotache

Al.I. Cuza University of Iași

Faculty of Economics and Business Administration

Department of Accounting, Information ystems andtatistics


2/17

R script associated with thispresentation

!"a#functions#for#$As#strings#etc.%

&ttp'(()drv.ms()E)m*)i

http://1drv.ms/1E1m81ihttp://1drv.ms/1E1m81i


3/17

"e# sites with R tutorials forsyste$ functions

&ttp'((+++.sr.&am.ac.u-(a/rs(%(r0function#list.&tmlort

&ttp'((+++.sr.&am.ac.u-(a/rs(%(r0functio

n#list.&tml

http://www.sr.bham.ac.uk/~ajrs/R/r-function_list.htmlhttp://www.sr.bham.ac.uk/~ajrs/R/r-function_list.htmlhttp://www.sr.bham.ac.uk/~ajrs/R/r-function_list.htmlhttp://www.sr.bham.ac.uk/~ajrs/R/r-function_list.html


4/17

%wo $ain types of $issing alues

$A'◦ Stands for Not Available

◦ Is the equivalent of NULL in relational databases

◦ When importing data from Excel, tabdelimited files, etc!, usuall"

un#no$n values are represented b" NA%s

◦ Not to be confounded $ith &NA& string '$hich sometimes occurs

$hen importing(

◦ )ain function* is.na()

$U11'

◦ +ompletel" different from NULLs in relational databases

◦ Within a vector, an element can be NA but not NULL 'NULL is

atomic( if used inside a vector, a NULL element simpl"

dissapears


5/17

Function is.na

Create a very simple vector'

> y is.na(y)

[1] FALSE FALSE FALSE TRUE


6/17

Function na.fail

Function na.fail c&ec-s if t&ere are NA values in a dataset2na.fail +ill generate an error if t&ere is at least one NA

+it&in one of t&e columns of t&e data set

Data frames student'gi, patientdata, $pi,

Fuel()ciency.new, %oyota*orolla do not containNA

values

> na.fail(st!"nt#$i) na%" a$" sc&'las&i la*#ass"ss%"nt final#$a!"

1++1 '"sc . asil" 23 S'cial /in" 0.++

1++2 an's . A!iana 10 St!i1 F'at" *in" 0.1++3 4'5ac6 . 's"f 21 St!i2 E7c"l"nt 0.8

1++ /a*a!a$ . 9aia 22 9"it /in" 0.++

1++ ' . 'n 31 St!i1 Sla* :.++


7/17

Function na.fail +cont.

Data frame leadership contains at least one $A value,so na.fail +ill generate an error'

> na.fail(l"a!"s&i)

E' in na.fail.!"falt(l"a!"s&i) ; %issin$5al"s in '*"ct

> l"a!"s&i %ana$" !at" c'nty $"n!" a$" =1 =2 =3= =

1 1 2+1+1+2 US 9 32

2 2 1001+2? US F 3 2

3 3 10?1+1 U4 F 2 3 2

2+++121+ U4 9 0 3 3


8/17

*hec2 NA3s for range ofele$ents

Display, for eac& student, if t&e e0mail is missing ornot

> &"a!(st!s2+1)

> is.na(st!s2+1[,@"%ail@])

Display only t&e students +it& misssing e0mail

address'

> st!s2+1[is.na(st!s2+1"%ail),]

Display, for eac& oservation, if variales 4)'45 are$A in data frame leaders&ip'

> is.na(l"a!"s&i[,:;1+]) =1 =2 =3 = =

[1,] FALSE FALSE FALSE FALSE FALSE




9/17

*ounting NA3s

Counting t&e numer if $A values +it&in anentire data frame is possile +it& function sumand t&e follo+ing synta6's%(is.na(t&".!ata.fa%"))

7o+ many $A values are t&e in data frameleadership8

> s%(is.na(l"a!"s&i))

[1] 2

7o+ many $A values are t&e in data framecomp8

> s%(is.na(c'%))


10/17

Function complete.cases

Display oservations(ro+s +&ic& &ave at least one$A

> l"a!"s&i[Bc'%l"t".cas"s(l"a!"s&i),]

%ana$" !at" c'nty $"n!" a$" =1 =2 =3= =

2+++121+ U4 9 0 3 3 NA NA

> c'%[Bc'%l"t".cas"s(c'%),]

Counting &o+ many oservations(ro+s &ave atleast one $A and &o+ many &ave no $As 9arecomplete cases:

> ta*l"(c'%l"t".cas"s(l"a!"s&i))

FALSE TRUE1


11/17

*ounting4displaying NA3s foraria#les and ranges

7o+ many students &ave no e0mail address 8◦ Using sum!!!

> s%(is.na(st!s2+1"%ail))

[1] 1:18

◦ !!!or table

> ta*l"(is.na(st!s2+1"%ail))

FALSE TRUE

?8 1:18

Display, for eac& oservation, oservations in+&ic& at least one value of variales 5/657 is $Ain data frame leadership

> l"a!"s&i[Bc'%l"t".cas"s(l"a!"s&i[:;1+]),]

%ana$" !at" c'nty $"n!" a$" =1 =2 =3


12/17

NULLs

Completely di;erent from dataases 9$A is prettyclose to t&e concept of $U11 in relational dataases

5.Cit&.nll =)> ) ? " 5 @


13/17

NULLs +cont.> l"n$t&(5.Cit&.na)

=)> @> l"n$t&(5.Cit&.nll)

=)> 5

> s%(5.Cit&.na)

=)> $A> s%(5.Cit&.nll)

=)> )

In a data frame, a variale(column set to $U11 alsodissapears

> na%"s(a!l2+13#st!)

=)> $r $umeren atricol Email

> a!l2+13#st!N na%"s(a!l2+13#st!)

=)> $umeren atricol Email


14/17

Functions for $anaging stringaria#les

Base %

◦ nchar ◦ substr

◦ strsplit

◦ paste - paste. - sprintf

ac-age stringr◦ str/c'( string concatenation 0 paste'(

◦ str/length'( number of characters 0 nchar'(

◦ str/sub'( extracts substrings 0 substring'(

◦ str/dup'( duplicates characters 0 no equivalent

◦ str/trim'( removes leading and trailing $hitespace 0 noequivalent

◦ str/pad'( pads a string 0 no equivalent

◦ str/$rap'( $raps a string paragraph 0 str$rap'(

◦ str/trim'( trims a string 0 no equivalent

◦ $ord '( 1 extracts $ords from a string 0 no equivalent


15/17

So$e we# pages for processingstrings in R

aston anc&ez 0 7andling androcessing trings in %

&ttp'((gastonsanc&ez.com(7andling#and#r

ocessing#trings#in#%.pdf o&n yles


16/17

Regular expressions

ital for te6t(string(+e searc&ing

Implemented in almost every programminglanguage

In J1 t&e asic mec&anist is rudimentar andased on operators' 1IKE, I1IKE, II1A% 3L

% &as full support for regular e6pressions

◦ 2unctions in base 3*

grep, grepl,

su, gsu,

rege6pr, grege6pr

◦ 2unctions in pac#age stringr *

strdetect

stre6tract, stre6tractall, strmatc&, strmatc&all

strlocate, strlocateall

strreplace, strreplaceall

strsplit, strsplitM6ed


17/17

"e# sites4ideo8tutorials for regularexpression +generally and R speci9c

Basics of regular e6pressions 9in generaland in %:

&ttp'((+++.re6egg.com(rege604uic-start

.&tml&ttp'((+++.r0loggers.com(regular0e6pres

sion0and0associated0functions0in0r(

&ttp'((+++.r0loggers.com(r0tal-0on0regular0e6pressions0rege6(

%egular E6pressions

&ttps'((+++.youtue.com(+atc&8vN$v7/O
http://www.rexegg.com/regex-quickstart.htmlhttp://www.rexegg.com/regex-quickstart.htmlhttp://www.r-bloggers.com/regular-expression-and-associated-functions-in-r/http://www.r-bloggers.com/regular-expression-and-associated-functions-in-r/http://www.r-bloggers.com/r-talk-on-regular-expressions-regex/http://www.r-bloggers.com/r-talk-on-regular-expressions-regex/https://www.youtube.com/watch?v=NvHjYOilOf8https://www.youtube.com/watch?v=NvHjYOilOf8https://www.youtube.com/watch?v=NvHjYOilOf8http://www.r-bloggers.com/r-talk-on-regular-expressions-regex/http://www.r-bloggers.com/r-talk-on-regular-expressions-regex/http://www.r-bloggers.com/regular-expression-and-associated-functions-in-r/http://www.r-bloggers.com/regular-expression-and-associated-functions-in-r/http://www.rexegg.com/regex-quickstart.htmlhttp://www.rexegg.com/regex-quickstart.html

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04a Functions for NAs Strings Etc