[R] Help avoiding setting column type two times

[David Winsemius]

> On Nov 30, 2017, at 6:27 AM, Martin Møller Skarbiniks Pedersen <traxplayer at gmail.com> wrote:
> 
> Hi,
>  I think and hope this a good place to ask for code review for a R
> beginners?
> 
>  I have made a R script which generates a dataset based on 2009 danish
> referendum and it does work.
> 
>  But I think the code could be better and I would any comments how the
> code can be improved.
>  At least I would like to know how I avoid converting several of the
> columns to factors in the end of the code?
> 
> Description of the code:
> 
>  It reads a lot of xml-files from ../raw/ and saves a data.frame with
> information
> from these xml-files.
> 
>  In the ../raw/ directiory I have placed the xml-files which I got from
> "Statistics Denmark"
>  I have also put these xml-files on my website and they can be download
> freely from http://20dage.dk/R/referendum-2009/raw.tar.gz
> 
>  The code is below but I have also put the code at this place:
> http://20dage.dk/R/referendum-2009/convert_from_xml.R
> 
> Best Regards
> Martin M. S. Pedersen
> 
> -------
> library(xml2)
> 
> convert_one_file <- function(url) {
>    x <- read_xml(url)
> 
>    Sted <- xml_find_first(x, ".//Sted")
>    StedType <- xml_attr(Sted, "Type")
>    StedTekst <- xml_text(Sted)
> 
>    Parti <- xml_find_all(x, ".//Parti")
>    PartiId <- xml_attr(Parti, "Id")
>    PartiBogstav <- xml_attr(Parti, "Bogstav")
>    PartiNavn <- xml_attr(Parti, "Navn")
> 
> 
>    StemmerAntal <- xml_attr(Parti, "StemmerAntal")
>    Stemmeberettigede <- xml_integer(xml_find_first(x,
> ".//Stemmeberettigede"))
>    DeltagelsePct <- xml_double(xml_find_first(x, ".//DeltagelsePct"))
>    IAltGyldigeStemmer <- xml_integer(xml_find_first(x,
> ".//IAltGyldigeStemmer"))
>    BlankeStemmer <- xml_integer(xml_find_first(x, ".//BlankeStemmer"))
>    AndreUgyldigeStemmer <- xml_integer(xml_find_first(x,
> ".//AndreUgyldigeStemmer"))
> 
>    data.frame(cbind(StedType, StedTekst, PartiId, PartiBogstav, PartiNavn,
>                 StemmerAntal, Stemmeberettigede, DeltagelsePct,
> IAltGyldigeStemmer,
>       BlankeStemmer, AndreUgyldigeStemmer), stringsAsFactors = FALSE)

The construction `data.frame(cbind( ...` is a serious source of potential error. The cbind coerces to matrix class which also then coerces to a single atomic class, either numeric or character. Factors loose all their meaning. Dates get messed up. Error ensues. Better would be:

 data.frame( StedType, StedTekst, PartiId, PartiBogstav, PartiNavn,
             StemmerAntal, Stemmeberettigede, DeltagelsePct,
             IAltGyldigeStemmer, BlankeStemmer, AndreUgyldigeStemmer,
             stringsAsFactors = FALSE)

-- 
David.


> }
> 
> raw_path <- "../raw"
> filenames <- dir(path = raw_path, pattern = "fintal_.*", full.names = T)
> 
> result <- data.frame(StedType = factor(),
>                     StedTekst = character(),
>                     PartiId   = factor(),
>                     PartiBogstav = factor(),
>                     PartiNavn    = factor(),
>                     StemmerAntal = integer(),
>                     Stemmeberettigede = integer(),
>                     DeltagelsePct = numeric(),
>                     IAltGyldigeStemmer = integer(),
>                     BlankeStemmer = integer(),
>                     AndreUgyldigeStemmer = integer(),
>                     stringsAsFactors = FALSE)
> 
> for (i in 1:length(filenames)) {
>    #cat(paste0(filenames[i],"\n"))
>    returnCode <-  tryCatch({
>       result <- rbind(result, convert_one_file(filenames[i]))
>    }, error = function(e) {
>       cat(paste0(filenames[i]," failed:\n",e,"\n"))
>    })
> }
> 
> result$StedType <- as.factor(result$StedType)
> result$PartiId <- as.factor(result$PartiId)
> result$PartiBogstav <- as.factor(result$PartiBogstav)
> result$PartiNavn <- as.factor(result$PartiNavn)
> result$StemmerAntal <- as.integer(result$StemmerAntal)
> result$Stemmeberettigede <- as.integer(result$Stemmeberettigede)
> result$DeltagelsePct <- as.numeric(result$DeltagelsePct)
> result$IAltGyldigeStemmer <- as.integer(result$IAltGyldigeStemmer)
> result$BlankeStemmer <- as.integer(result$BlankeStemmer)
> result$AndreUgyldigeStemmer <- as.integer(result$AndreUgyldigeStemmer)
> str(result)
> save(result, file = "folkeafstemning2009.Rdata")
> 
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> 
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David Winsemius
Alameda, CA, USA

'Any technology distinguishable from magic is insufficiently advanced.'   -Gehm's Corollary to Clarke's Third Law