R help - May 2011 - R as.numeric()

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


-- 
The University of Edinburgh is a charitable body, registered in
Scotland, with registration number SC005336.

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

On 24 May 2011, at 10:20 PM, Lutz Fischer wrote:
> n<-data.matrix(s);
> > s[1,2]
> [1] 30.94346629 # 3136 Levels: 0.026307482
> turned into:
> > n[1,2]
> [1] 3020
Dear Lutz, ?3020? is the factor level associated with 30.94346629, in turn
generated by importing with strings in the column

Try passing "na.strings = ?n/a? ? into the read.xls function to avoid the
problem

If not, then as.numeric(as.character(datafulloffactors) will work

as.numeric sees the factor levels: as.character forces as.numeric to see the
?labels?

t