[R] R as.numeric()

[Ista Zahn]

This is a FAQ:

http://cran.r-project.org/doc/FAQ/R-FAQ.html#How-do-I-convert-factors-to-numeric_003f

Please try there before posting a question to the list.

Best,
Ista
On Tue, May 24, 2011 at 5:33 PM, David Scott <d.scott at auckland.ac.nz> wrote:
> On 25/05/2011 9:20 a.m., Lutz Fischer wrote:
>>
>> Hi,
>>
>> I have a bit of a problem with as.numeric or as.double.
>>
>> I read in an excel-file (either xlsx::read.xlsx2 or gdata::read.xls).
>> Select a subset and then try to make it numeric:
>>
>>
>> # read in the excel-file
>> alldata<-read.xlsx2("input.xls",1)
>> # select the subset
>> s<-subset(alldata, select=c("cI","cII","cIII","cIV","cV"))
>> # unluckily we have "n/a" for missing values in the file - so we turn it
>> into "proper" missing values
>> s[s == "n/a"]<-NA
>>
>> n<-data.matrix(s);
>>
>>
>>
>>
>> The problem I have is that it does not convert the date the way I would
>> expect.
>>
>> just as an example:
>>  > s[1,2]
>> [1] 30.94346629
>> 3136 Levels: 0.026307482 0.028239812 0.02849896 0.029054564 0.029540352
>> 0.030248034 0.030841352 0.032966308 ... n/a
>>
>> turned into:
>>  > n[1,2]
>> [1] 3020
>>
>> And I would like to have there 30.94346629 as well. I assume that has to
>> do with the "Levels" attribute - but not sure what to make of these in
>> the first place.
>>
>> I also tried to convert each value on its own:
>>
>> #make some space that holds the actual numeric data
>> n <- array(dim=c(length(s[,1]),length(s)))
>> # now turn everything into doubles
>> for (c in 1:length(s)) {
>> for (r in 1:length(s[,1])) {
>> n[r,c]<-as.double(s[r,c])
>> }
>> }
>>
>> but that gave the same result - just a lot slower.
>>
>>
>>
>> Thanks
>> Lutz
>>
>>
> Your problem is the conversion to factors when the data is read. Use
>
> options(stringsAsFactors = FALSE)
>
> before you read the data, then the mixed columns of numeric and missing will
> be read as character data and the conversion to numeric will go as you
> expect. (But I haven't tested this.)
>
> David Scott
> --
> _________________________________________________________________
> David Scott     Department of Statistics
>                The University of Auckland, PB 92019
>                Auckland 1142,    NEW ZEALAND
> Phone: +64 9 923 5055, or +64 9 373 7599 ext 85055
> Email:  d.scott at auckland.ac.nz,  Fax: +64 9 373 7018
>
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>



-- 
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org