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Chapter6. Graphsandplots
40
6.2 Plottinggraphsfromscripts
Whenworkingwithscripts,youmaywanttohaveagraphshownontoyourdisplayorsavedintoa
file.Infact,ifinyourusualworkflowyoufindyourselfcreatingsimilargraphsoverandoveragain,
youmightwanttoconsider theoptionofwritingascriptwhichautomatesthisprocessfor you.
Gretlgivesyoutwomaintoolsfordoingthis: oneisacommandcalledgnuplot,whosemainuse
is tocreatestandardplotquickly. . Theotheroneis s theplotcommandblock, whichhasamore
elaboratesyntaxbutoffersyoumorecontrolonoutput.
Thegnuplotcommand
ThegnuplotcommandisdescribedatlengthintheGretlCommandReferenceandtheonlinehelp
system. Here,wejustsummarizeitsmainfeatures: basically,itconsistsofthegnuplotkeyword,
followedbyalistofitems,tellingthecommandwhatyouwantplottedandalistofoptions,telling
ithowyouwantitplotted.
Forexample,theline
gnuplot y1 1 y2 x
willgiveyouabasicXYplotofthetwoseriesy1andy2ontheverticalaxisversustheseriesxon
thehorizontalaxis. Ingeneral,theargumentstothegnuplotcommandisalistofseries,thelast
ofwhichgoesonthex-axis,whilealltheotheronesgo onto they-axis. . Bydefault, , thegnuplot
commandgivesyouascatterplot. Ifyoujusthaveonevariableonthey-axis, , thengretlwillalso
drawatheOLSinterpolation,ifthefitisgoodenough.2
Severalaspectsofthebehaviordescribedabovecanbemodified.Youdothisbyappendingoptions
tothecommand.Mostoptionscanbebroadlygroupedinthreecategories:
1. Plotstyles: wesupportpoints s (thedefaultchoice),lines,linesandpoints together, andim-
pulses(verticallines).
2. Algorithmforthefittedline: : hereyoucanchoosebetweenlinear,quadraticandcubicinter-
polation,butalsomoreexoticchoices,suchassemi-log,inverseorloess(non-parametric).Of
course,youcanalsoturnthisfeatureoff.
3. Inputandoutput: : you u canchoosewhether r youwantyour graphonyour computer screen
(andpossiblyusethein-builtgraphicalwidgettofurthercustomizeit— seeabove,page37),
orrathersaveittoafile. Wesupportseveralgraphicalformats,amongwhichPNGandPDF,
tomakeiteasytoincorporateyourplotsintotextdocuments.
ThefollowingscriptusestheAWMdatasettoexemplifysometraditionalplotsinmacroeconomics:
open AWM.gdt t --quiet
# --- - consumption and income, different styles s ------------
gnuplot PCR YER
gnuplot PCR YER --output=display
gnuplot PCR YER --output=display --time-series
gnuplot PCR YER --output=display --time-series s --with-lines
# --- - Phillips’ curve, different fitted lines s -------------
gnuplot INFQ Q URX X --output=display
2
Thetechnicalconditionforthisisthatthetwo-tailedp-valuefortheslopecoefficientshouldbeunder10%.
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Chapter6. Graphsandplots
41
gnuplot INFQ Q URX X --suppress-fitted d --output=display
gnuplot INFQ Q URX X --inverse-fit --output=display
gnuplot INFQ Q URX X --loess-fit --output=display
FIXME:commentontheabove
Formoredetail,consulttheGretlCommandReference.
Theplotcommandblock
TheplotenvironmentisawaytopassinformationtoGnuplotinamorestructuredway,sothat
customizationofbasicplotsbecomeseasier.Ithasthefollowingcharacteristics:
Theblock starts withtheplotkeyword,followedbyarequiredparameter: : thenameofalist, , a
singleseriesoramatrix. Thisparameterspecifiesthedatatobeplotted. Thestartinglinemaybe
prefixedwiththesavename <-apparatustosaveaplotasaniconintheGUIprogram. . Theblock
endswithend plot.
Insidetheblockyouhavezeroormorelinesofthesetypes,identifiedbyaninitialkeyword:
option: specifyasingleoption(detailsbelow)
options: specifymultipleoptionsonasingleline;ifmorethanoneoptionisgivenonaline,the
optionsshouldbeseparatedbyspaces.
literal: acommandtobepassedtognuplotliterally
printf: aprintfstatementwhoseresultwillbepassedtognuplotliterally;thisallowstheuseof
stringvariableswithouthavingtoresortto@-stylestringsubstitution.
Theoptions availablearebasically those e of thecurrent gnuplot command, but witha fewdif-
ferences. Foronethingyoudon’tneedtheleadingdouble-dashinan"option"(or"options")line.
Besidesthat,
 Youcan’tusetheoption--matrix=whateverwithplot: : thatpossibilityishandledbypro-
vidingthenameofamatrixontheinitialplotline.
 The e --input=filename option is s not supported: : use e gnuplot for r the e casewhereyou’re
supplyingtheentireplotspecificationyourself.
 Theseveraloptionspertainingtothepresenceandtypeofafittedline,arereplacedinplot
byasingleoptionfitwhichrequiresaparameter. Supportedvaluesfortheparameterare:
none,linear,quadratic,cubic,inverse,semilogandloess.Example:
option fit=quadratic
As with gnuplot, thedefault is to showalinear fitinanX-Y scatter ifit’ssignificantatthe10
percentlevel.
Here’sa simpleexample, theplotspecification from the“bandplot”package, which shows s how
toachievethesameresultviathegnuplotcommandandaplot block, respectively—thelatter
occupiesafewmorelinesbutisclearer
gnuplot 1 2 3 4 4 --with-lines s --matrix=plotmat \
--suppress-fitted --output=display \
{ set t linetype e 3 3 lc c rgb "#0000ff"; set t title e "@title"; \
set nokey; ; set t xlabel l "@xname"; }
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Chapter6. Graphsandplots
42
plot plotmat
options with-lines fit=none
literal set linetype 3 lc c rgb b "#0000ff"
literal set nokey
printf "set title \"%s\"", title
printf "set xlabel \"%s\"", xname
end plot --output=display
Notethat--output=displayisappendedtoend plot;alsonotethatifyougiveamatrixtoplot
it’sassumedyouwanttoplotallthecolumns.Inaddition,ifyougiveasingleseriesandthedataset
istimeseries,it’sassumedyouwantatime-seriesplot.
FIXME:provideanexamplewithrealdata.
6.3 Boxplots
0
20000
40000
60000
80000
FAMINC
mean
Q3
Q1
median
minimum
maximum
outliers
Figure6.3:Sampleboxplot
Theseplots (after r Tukey andChambers) displaythe distribution ofa variable. . Thecentralbox
enclosesthemiddle50percentofthedata,i.e.itisboundedbythefirstandthirdquartiles. The
“whiskers”extendtofromeachendoftheboxforarangeequalto1.5timestheinterquartilerange.
Observationsoutsidethatrangeareconsideredoutliersandrepresentedviadots.Alineisdrawn
acrosstheboxatthemediananda“+”signidentifiesthemean—seeFigure6.3.
Inthecaseofboxplotswithconfidenceintervals,dottedlinesshowthelimitsofanapproximate90
percentconfidenceintervalforthemedian. Thisisobtainedbythebootstrapmethod,whichcan
takeawhileifthedataseriesisverylong. Fordetailsonconstructingboxplots,seetheentryfor
boxplotintheGretlCommandReference orusetheHelpbuttonthatappearswhenyouselectone
oftheboxplotitemsunderthemenuitem“View,Graphspecifiedvars”inthemaingretlwindow.
3
Togiveyouanintuitiveidea,ifavariableisnormallydistributed,thechancesofpickinganoutlierbythisdefinition
areslightlybelow0.7%.
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Chapter6. Graphsandplots
43
Factorizedboxplots
Anicefeaturewhichisquiteusefulfordatavisualizationistheconditional,orfactorizedboxplot.
Thistypeofplotallowsyouto examinethedistributionofavariableconditionalonthevalueof
somediscretefactor.
Asanexample,we’lluseoneofthedatasetssuppliedwithgretl,thatisrac3d,whichcontainsan
exampletaken fromCameronandTrivedi(2013)onthehealthconditions of5190people. . The
scriptbelowcomparestheunconditional(marginal)distributionofthenumberofillnessesinthe
past2weekswiththedistributionofthesamevariable,conditionalonageclasses.
open rac3d.gdt
# unconditional l boxplot
boxplot ILLNESS --output=display
# create e a discrete variable for age class:
# 0 0 = below 20, 1 = between 20 and d 39, , etc
series age_class = floor(AGE/0.2)
# conditional boxplot
boxplot ILLNESS age_class --factorized --output=display
Afterrunningthecodeabove,youshouldseetwographssimilarto Figure6.4. Bycomparingthe
marginalplot to o thefactorized one, , theeffect t of ageonthe mean number r ofillnesses is quite
evident: byjoiningthegreencrossesyougetwhatistechnicallyknownastheconditionalmean
function,orregressionfunctionifyouprefer.
0
1
2
3
4
5
ILLNESS
0
1
2
3
4
5
0
1
2
3
ILLNESS
age_class
Distribution of ILLNESS by age_class
Figure6.4:Conditionalandunconditionaldistributionofillnesses
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Chapter7
Joiningdatasources
7.1 Introduction
Gretlprovides two commands for adding datafrom fileto anexistingdataset in theprogram’s
workspace,namelyappendandjoin. Theappendcommand,whichhasbeenavailableforalong
time,isrelativelysimpleandisdescribedintheGretlCommandReference. Herewefocusonthe
join command, whichis muchmoreflexibleandsophisticated. . Thischapter r givesanoverview
ofthefunctionalityofjoin alongwithadetailedaccountofitssyntaxandoptions. . Weprovide
severaltoyexamplesanddiscussonereal-worldcaseatlength.
First, a noteonterminology: : in n thefollowing weusetheterms “left-hand” and “inner”to o refer
tothedatasetthatis alreadyinmemory, andtheterms“right-hand”and “outer”to referto the
datasetinthefilefromwhichadditionaldataaretobedrawn.
Twomainfeaturesofjoinareworthemphasizingattheoutset:
 “Key” ” variables can be used to match specific c observations s (rows) in theinner and outer
datasets,andthismatchneednotbe1to1.
 Arowfiltermaybeappliedtoscreenoutunwantedobservationsintheouterdataset.
Aswillbeexplainedbelow,thesefeaturessupportrathercomplexconcatenationandmanipulation
ofdatafromdifferentsources.
Afurtheraspectofjoinshouldbenoted—onethatmakesthiscommandparticularlyusefulwhen
dealingwithverylargedatafiles. Thatis,whengretlexecutesajoinoperationitdoesnot,ingen-
eral,readintomemorytheentirecontentoftheright-handsidedataset. Onlythosecolumnsthat
areactuallyneededfortheoperationarereadinfull. Thismakesjoinfasterandlessdemanding
ofcomputermemorythanthemethodsavailableinmostothersoftware.Ontheotherhand,gretl’s
asymmetricaltreatmentofthe“inner”and“outer”datasetsinjoinmayrequiresomegettingused
to,forusersofotherpackages.
7.2 Basicsyntax
Theminimalinvocationofjoinis
joinfilenamevarname
wherefilenameis thenameofa a datafile and varname is s the e name of aseries s to beimported.
Onlytwosortsofdatafilearesupportedatpresent: delimitedtextfiles(wherethedelimitermay
becomma, space, tabor semicolon)and “native”gretldatafiles (gdt or gdtb). . A A series named
varnamemayalreadybepresentintheleft-handdataset,butthatisnotrequired.Theseriestobe
importedmaybenumericalorstring-valued.Formostofthediscussionbelowweassumethatjust
asingleseriesisimportedbyeachjoincommand,butseesection7.7foranaccountofmultiple
imports.
Theeffectoftheminimalversionofjoinisthis: gretllooksforadatacolumnlabeledvarnamein
thespecifiedfile;ifsuchacolumnisfoundandthenumberofobservationsontherightmatches
thenumberofobservationsinthecurrentsamplerangeontheleft,thenthevaluesfromtheright
arecopiedinto therelevantrangeofobservations ontheleft. . Ifvarnamedoesnotalreadyexist
44
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Chapter7. Joiningdatasources
45
ontheleft,anyobservationsoutsideofthecurrentsamplearesetto NA;ifitexistsalreadythen
observationsoutsideofthecurrentsampleareleftunchanged.
Thecasewhereyouwanttorenameaseriesonimportishandledbythe--dataoption.Thisoption
hasonerequiredargument,thenamebywhichtheseriesisknownontheright. Atthispointwe
needtoexplainsomethingaboutright-handvariablenames(columnheadings).
Right-handnames
Weacceptoninputarbitrarycolumnheadingstrings,butifthesestringsdo notqualifyasvalid
gretlidentifiers they areautomatically converted, andin thecontextofjoin youmustusethe
converted names. . A A gretlidentifier muststartwithaletter, containnothingbut(ASCII)letters,
digitsandtheunderscorecharacter,andmustnotexceed31characters. Therulesusedinname
conversionare:
1. Skipanyleadingnon-letters.
2. Untilthe31-characterisreachedortheinputisexhausted:transcribe“legal”characters;skip
“illegal”charactersapartfromspaces; andreplaceoneor moreconsecutivespaceswithan
underscore, unless s thelastcharacter r transcribed d is an underscorein which case spaceis
skipped.
Intheunlikely event that this policyyieldsan emptystring, we replacetheoriginal withcoln,
where n is s replaced by the e 1-based index of thecolumn in question among g those e used in the
joinoperation. Ifyouareindoubtregardingtheconvertednameofagivencolumn,thefunction
fixname() canbeusedas acheck: : ittakes s theoriginalstringas anargumentandreturns the
convertedname.Examples:
? eval fixname("valid_identifier")
valid_identifier
? eval fixname("12. . Some e name")
Some_name
Returningtotheuseofthe--dataoption,supposewehaveacolumnheaded"12. Some name"
ontherightandwishtoimportitasx.Afterfiguringhowtheright-handnameconverts,wecando
join foo.csv x --data="Some_name"
Noright-handnames?
Somedatafileshavenocolumnheadings;theyjumpstraightintothedata(andyouneedtodeter-
minefromaccompanyingdocumentationwhatthecolumnsrepresent).Sincegretlexpectscolumn
headings,youhavetotakestepstogettheimportationright.Itisgenerallyagoodideatoinserta
suitableheaderrowintothedatafile.However,ifforsomereasonthat’snotpractical,youshould
givethe--no-headeroption,inwhichcasegretlwillnamethecolumnsontherightascol1,col2
andsoon. Ifyoudo o notdoeitherofthesethingsyouwilllikelylosethefirstrowofdata,since
gretlwillattempttomakevariablenamesoutofit,asdescribedabove.
7.3 Filtering
Rowsfromtheouter datasetcanbefilteredusingthe--filteroption. . Therequiredparameter
for this option n is a Booleancondition, thatis, anexpression which evaluatesto o non-zero (true,
includetherow)orzero(false,skiptherow)foreachoftheouterrows. Thefilterexpressionmay
includeanyofthefollowingterms:uptothree“right-hand”series(undertheirconvertednamesas
Chapter7. Joiningdatasources
46
explainedabove);scalarorstringvariablesdefined“ontheleft”;anyoftheoperatorsandfunctions
availableingretl(includinguser-definedfunctions);andnumericorstringconstants.
Hereareafewsimpleexamplesofpotentiallyvalidfilteroptions(assumingthatthespecifiedright-
handsidecolumnsarefound):
# 1. relationship between two o right-hand variables
--filter="x15<=x17"
# 2. comparison of f right-hand variable e with constant
--filter="nkids>2"
# 3. comparison of f string-valued d right-hand variable e with h string constant
--filter="SEX==\"F\""
# 4. filter on valid values of f a a right-hand variable
--filter=!missing(income)
# 5. compound condition
--filter="x < 100 && (x > 0 || | y y > 0)"
Notethatif youarecomparingagainstastringconstant(as inexample3above)itis necessary
toputthestringin“escaped”double-quotes(eachdouble-quoteprecededbyabackslash)so the
interpreterknowsthatFisnotsupposedtobethenameofavariable.
Itis safestto o enclosethe whole filter expression indoublequotes, however r this is notstrictly
requiredunlesstheexpressioncontainsspacesortheequalssign.
Ingeneral, an error isflaggedifamissing valueis encountered in aseriesreferencedinafilter
expression. Thisisbecausetheconditionthenbecomesindeterminate;takingexample2above,if
thenkidsvalueisNAonanygivenrowwearenotinapositiontoevaluatetheconditionnkids>2.
However,youcanusethemissing()function—orok(),whichisashorthandfor!missing()—if
youneedafilterthatkeysoffthemissingornon-missingstatusofavariable.
7.4 Matchingwithkeys
Thingsgetinterestingwhenwecometokey-matching. Thepurposeofthisfacilityisperhapsbest
introducedbyexample. Supposethat(aswithmanysurveyandcensus-baseddatasets)wehavea
datasetthatiscomposedoftwoormorerelatedfiles,eachhavingadifferentunitofobservation;
forexamplewehavea“persons”datafileanda“households”datafile. Table7.1showsasimple,
artificial case. . The e file people.csv contains s a a uniqueidentifier for the individuals, , pid. . The
householdsfile,hholds.csv,containstheuniquehouseholdidentifierhid,whichisalsopresent
inthepersonsfile.
As a a first exampleof join with keys, , let’s s add the e household-level variablexh to o the e persons
dataset:
open people.csv --quiet
join hholds.csv xh h --ikey=hid
print --byobs
Thebasickeyoptionisnamedikey;thisindicates“innerkey”,thatis,thekeyvariablefoundinthe
left-handorinnerdataset.Bydefaultitisassumedthattheright-handdatasetcontainsacolumnof
thesamename,thoughaswe’llseebelowthatassumptioncanbeoverridden.Thejoincommand
abovesays,findaseriesnamedxhintheright-handdatasetandaddittotheleft-handone,using
thevalues of hid to match rows. . Looking g at thedatainTable 7.1wecan seehow thisshould
work. Persons1and2arebothmembersofhousehold1,sotheyshouldbothgetvaluesof1for
xh;persons3and4aremembersofhousehold2,sothatxh =4; andsoon. . Notethattheorder
Chapter7. Joiningdatasources
47
inwhichthekeyvaluesoccurontheright-handsidedoesnotmatter. Thegretloutputfromthe
printcommandisshowninthelowerpanelofTable7.1.
people.csv
hholds.csv
pid,hid,gender,age,xp
hid,country,xh
1,1,M,50,1
1,US,1
2,1,F,40,2
6,IT,12
3,2,M,30,3
3,UK,6
4,2,F,25,2
4,IT,8
5,3,M,40,3
2,US,4
6,4,F,35,4
5,IT,10
7,4,M,70,3
8,4,F,60,3
9,5,F,20,4
10,6,M,40,4
pid
hid
xh
1
1
1
2
1
1
3
2
4
4
2
4
5
3
6
6
4
8
7
4
8
8
4
8
9
5
10
10
6
12
Table7.1: TwolinkedCSVdatafiles,andtheeffectofajoin
Notethatkeyvariablesaretreatedconceptuallyasintegers. Ifaspecifiedkeycontainsfractional
valuesthesearetruncated.
Twoextensionsofthebasickeymechanismareavailable.
 Iftheouterdatasetcontainsarelevantkeyvariablebutitgoesunderadifferentnamefrom
theinner key,youcanusethe--okeyoptiontospecifytheouter key. . (Aswithotherright-
handnames,thisdoesnothavetobeavalidgretlidentifier.) So,forexample,ifhholds.csv
containedthehidinformation,butunderthenameHHOLD,thejoin commandabovecould
bemodifiedas
join hholds.csv xh --ikey=hid --okey=HHOLD
 Ifasinglekeyisnotsufficienttogeneratethematchesyouwant,youcanspecifyadoublekey
intheformoftwoseriesnamesseparatedbyacomma;inthiscasetheimportationofdatais
restrictedtothoserowsonwhichbothkeysmatch.Thesyntaxhereis,forexample
join foo.csv x --ikey=key1,key2
Again, the--okeyoptionmaybeusedifthecorrespondingright-handcolumnsarenamed
differently. Thesamenumber r ofkeys mustbegivenontheleftandtheright, butwhen n a
Chapter7. Joiningdatasources
48
doublekeyisused and onlyoneofthekeynames differs ontheright,thenamethatis in
commonmaybeomitted(althoughthecommaseparatormustberetained).Forexample,the
secondofthefollowinglinesisacceptableshorthandforthefirst:
join foo.csv x --ikey=key1,Lkey2 --okey=key1,Rkey2
join foo.csv x --ikey=key1,Lkey2 --okey=,Rkey2
Thenumberofkey-matches
TheexampleshowninTable7.1isaninstanceofa1to1match: applyingthematchingcriterion
producesexactlyonevalueofthevariablexhcorrespondingtoeachrowoftheinnerdataset.Two
otherpossibilitiesarise:itmaybethatsomerowsintheinnerdatasethavenomatchontheright,
and/orsomerowsonthelefthavemultiplematchesontheright.Thelattercase(“1tonmatching”)
isaddressedindetailinthenextsection;herewediscusstheformer.
Thecasewherethere’snomatchontherightishandleddifferentlydependingonwhetherthejoin
operationisaddinganewseriesto theinner datasetor modifyinganexistingone. . Ifit’s s anew
series,thentheunmatchedrowsautomaticallygetNAfortheimporteddata.If,ontheotherhand,
thejoinispullinginvaluesforaseriesthatisalreadypresentontheleft,onlymatchedrowswill
beupdated—orinotherwords,wedonotoverwiteanexistingvalueontheleftwithNAinthecase
wherethere’snomatchontheright.
Thesedefaultsmaynotproducethedesiredresultsineverycasebutgretlprovidesthemeansto
modifytheeffectifneedbe.Wewillillustratewithtwoscenarios.
First, consider adding anewseries recording“number ofhours worked”whentheinner dataset
containsindividualsandtheouterfilecontainsdataonjobs. Ifanindividualdoesnotappear r in
thejobsfile,wemaywanttotakeherhoursworkedasimplicitlyzeroratherthanNA.Inthiscase
gretl’smisszero()functioncanbeusedtoturnNAinto0intheimportedseries.
Second,considerupdatingaseriesviajoin,whentheouterfileispresumedtocontainallavailable
updatedvalues,suchthat“nomatch”shouldbetakenasanimplicitNA.Inthiscasewewantthe
(presumablyout-of-date)valuesonanyunmatchedrowstobeoverwrittenwithNA.Lettheseries
inquestionbecalledx(bothontheleftandtheright)andletthecommonkeybecalledpid. The
solutionisthen
join update.csv tmpvar --data=x --ikey=pid
x = tmpvar
Asanewvariable, tmpvarwillgetNA forallunmatchedrows; wethentranscribeitsvaluesinto
x. Inamorecomplicatedcaseonemightusethesmplcommandtolimitthesamplerangebefore
assigningtmpvartox,orusetheconditionalassignmentoperator?:.
Onefurtherpointshouldbementionedhere.Givensomemissingvaluesinanimportedseriesyou
maysometimeswanttoknowwhether(a)theNAswereexplicitlyrepresentedintheouterdatafile
or (b)theyarosedueto “no match”. . Youcanfind d this outbyusing amethod described in the
followingsection,namelythecountvariantoftheaggregationoption: thiswillgiveyouaseries
with0valuesforallandonlyunmatchedrows.
7.5 Aggregation
Inthecaseof1tonmatchingofrows(n>1)theusermustspecifyan“aggregationmethod”;that
is,amethodformappingfromnrowsdowntoone. Thisishandledbythe--aggroptionwhich
requiresasingleargumentfromthefollowinglist:
Chapter7. Joiningdatasources
49
Code
Valuereturned
count
countofmatches
avg
meanofmatchingvalues
sum
sumofmatchingvalues
min
minimumofmatchingvalues
max
maximumofmatchingvalues
seq:i
thei
th
matchingvalue(e.g.seq:2)
min(aux)
minimumofmatchingvaluesofauxiliaryvariable
max(aux)
maximumofmatchingvaluesofauxiliaryvariable
Notethatthecountaggregationmethodisspecial,inthatthereisnoneedfora“dataseries”on
theright;theimportedseriesissimplyafunctionofthespecifiedkey(s). Alltheother r methods
requirethat“actualdata”arefound on theright. . Alsonotethatwhen n count t isused, thevalue
returnedwhennomatchisfoundis(asonemightexpect)zeroratherthanNA.
Thebasicuseoftheseqmethodisshownabove:followingthecolonyougiveapositiveintegerrep-
resentingthe(1-based)positionoftheobservationinthesequenceofmatchedrows.Alternatively,
anegativeintegercanbeusedtocountdownfromthelastmatch(seq:-1selectsthelastmatch,
seq:-2thesecond-lastmatch,andsoon). Ifthespecifiedsequencenumberisoutofboundsfora
givenobservationthismethodreturnsNA.
ReferringagaintothedatainTable7.1,supposewewanttoimportdatafromthepersonsfileinto
adatasetestablishedathouseholdlevel. Here’sanexamplewhereweusetheindividualagedata
frompeople.csvtoaddtheaverageandminimumageofhouseholdmembers.
open hholds.csv --quiet
join people.csv avgage --ikey=hid --data=age --aggr=avg
join people.csv minage --ikey=hid --data=age --aggr=min
Here’safurtherexamplewhereweaddtothehouseholddatathesumofthepersonaldataxp,with
thetwistthatweapplyfilterstogetthesumspecificallyforhouseholdmembersundertheageof
40,andforwomen.
open hholds.csv --quiet
join people.csv young_xp --ikey=hid --filter="age<40" --data=xp p --aggr=sum
join people.csv female_xp --ikey=hid --filter="gender==\"F\"" --data=xp --aggr=sum
Thepossibilityofusinganauxiliaryvariablewiththeminandmaxmodesofaggregationgivesextra
flexibility.Forexample,supposewewantforeachhouseholdtheincomeofitsoldestmember:
open hholds.csv --quiet
join people.csv oldest_xp --ikey=hid --data=xp --aggr=max(age)
7.6 String-valuedkeyvariables
Theexamplesaboveusenumericalvariables(householdandindividualIDnumbers)inthematch-
ingprocess.Itisalsopossibletousestring-valuedvariables,inwhichcaseamatchmeansthatthe
stringvaluesofthekeyvariablescompareequal(withcasesensitivity). Whenusingdoublekeys,
youcanmixnumericalandstringkeys,butnaturallyyoucannotmixastringvariableontheleft
(viaikey)withanumericaloneontheright(viaokey),orviceversa.
Here’sasimpleexample. Supposethatalongsidehholds.csvwehaveafilecountries.csvwith
thefollowingcontent:
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