[R] Remove non-numerical columns from data frame

[Henrik Bengtsson]

On Sat, Jul 26, 2008 at 9:35 AM, Peter Dalgaard
<p.dalgaard at biostat.ku.dk> wrote:
> Henrique Dallazuanna wrote:
>>
>> Try this:
>>
>> x <- data.frame(A=c(10,20), B = c("a", "b"), C = c(20,30))
>> x[sapply(x, is.numeric)]
>>
>>
>
> Yes, and read ?Extract to clear up the confusion between data$vol and
> data[257] and data[[257]] (Section on "Recursive (list-like) objects:").
> Also, ?Extract.data.frame.

...and read up how you can use argument 'colClasses' in read.table()
to read/skip selected columns from a tabular data file.  Is that how
you get your data.frame in the first place?!

/Henrik

>
>> On Sat, Jul 26, 2008 at 11:19 AM, Markus Mühlbacher <muehliman at yahoo.com>
>> wrote:
>>
>>>
>>> Hello,
>>>
>>> My question sounds simple, but as I am desperatly searchin for a solution
>>> I am
>>> asking you all. :)
>>>
>>> I try to filter out all non-numeric columns of a data frame using a for
>>> loop
>>> to go through all columns. My if clause looks like this:
>>>
>>>        for(j in 1:length(data)) {
>>>
>>>                ...
>>>                if(!is.numeric(data[j])) skip <- "not numeric")
>>>                ...
>>>        }
>>>
>>> When I do: is.numeric(data$vol) i get TRUE as result:
>>> unfortunately this is not applicable in a for loop, because i need to go
>>> through all of the columns using j.
>>> I also tried to paste data$ and the name of the column , but this is
>>> always a
>>> character.
>>>
>>> When I do: is.numeric(data[257]) i get FALSE as result
>>> (257 is the corresponding column index to "vol")
>>>
>>
>
>
> --
>  O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
>  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
> (*) \(*) -- University of Copenhagen   Denmark      Ph:  (+45) 35327918
> ~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)              FAX: (+45) 35327907
>
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