R help - Aug 2009 - Issues with factors with duplicate (empty) levels

Hello!

I imported a DJI survey[1] from an SPSS file. When looking at some of
the variables, I noticed problems with the `table` function and similar.
It seems to be caused by duplicate levels which are generated from the
value labels. Not all values have labels, so those who don?t get an
empty string as the level, which leads to duplicates.

I hope the code and output below illustrates the problem. Is it possible
to prevent this? I?d still like to use the labels, so using numeric
vectors instead of factors is not the best solution.

Regards,
Frederik

> library(foreign)
> Data <- read.spss("js2003_16_29_db.sav", to.data.frame=TRUE,
reencode="latin1")
> table(Data$J203_A)
?berhaupt nicht wichtig                                                 
                     35                    2256                       0 
                                                                        
                      0                       0                       0 
           sehr wichtig         Mehrfachnennung 
                   4660                       0 
> table(as.numeric(Data$J203_A))
   1    2    3    4    5    6    7 
  35   39   84  227  626 1280 4660 
> is.factor(Data$J203_A)
[1] TRUE
> levels(Data$J203_A)
[1] "?berhaupt nicht wichtig" " "                      
[3] " "                       " "                      
[5] " "                       " "                      
[7] "sehr wichtig"            "Mehrfachnennung"        




[1] http://213.133.108.158/surveys/index.php?m=msw,0&sID=54
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Hello again,

Just for your information, I think I found a way to work around the
problem described below. I don?t know if it?s the most elegant way, but
it seems to work.

Am Mittwoch, den 26.08.2009, 11:55 +0200 schrieb Frederik
Elwert:
> Hello!
> 
> I imported a DJI survey[1] from an SPSS file. When looking at some of
> the variables, I noticed problems with the `table` function and similar.
> It seems to be caused by duplicate levels which are generated from the
> value labels. Not all values have labels, so those who don?t get an
> empty string as the level, which leads to duplicates.
> 
> I hope the code and output below illustrates the problem. Is it possible
> to prevent this? I?d still like to use the labels, so using numeric
> vectors instead of factors is not the best solution.
> 
> Regards,
> Frederik
> 
> 
> > library(foreign)
> > Data <- read.spss("js2003_16_29_db.sav",
to.data.frame=TRUE,
> reencode="latin1")
> > table(Data$J203_A)
> 
> ?berhaupt nicht wichtig                                                 
>                      35                    2256                       0 
>                                                                         
>                       0                       0                       0 
>            sehr wichtig         Mehrfachnennung 
>                    4660                       0 
> > table(as.numeric(Data$J203_A))
> 
>    1    2    3    4    5    6    7 
>   35   39   84  227  626 1280 4660 
> > is.factor(Data$J203_A)
> [1] TRUE
> > levels(Data$J203_A)
> [1] "?berhaupt nicht wichtig" " "                      
> [3] " "                       " "                      
> [5] " "                       " "                      
> [7] "sehr wichtig"            "Mehrfachnennung"        
	for (i in 1:ncol(Data)){
	    if (is.factor(Data[,i])){
                lvl <- levels(JS2003[,i])
	        if (" " %in% lvl){
	            empty <- lvl == " "
	            lvl[empty] <- (1:length(lvl))[empty]
    	        levels(Data[,i]) <- lvl
	        }
	    }
	}
> table(Data$J203_A)
?berhaupt nicht wichtig                       2                       3 
                     35                      39                      84 
                      4                       5                       6 
                    227                     626                    1280 
           sehr wichtig         Mehrfachnennung 
                   4660                       0