Re: [R] Combining logical operators to extract columns from a dataframe

From: Peter Dalgaard <p.dalgaard_at_biostat.ku.dk>
Date: Wed, 26 Mar 2008 00:41:02 +0100

mtb954_at_gmail.com wrote:
> Hi R-helpers,
>
> I have a dataframe (called data) with 100 columns, the columns of which are
> named with integers ranging from 1900 to 1999.
>
> I wish to extract those columns which names are >=1950 and <=1970.
>
> I tried:
>
> data2<-subset(data,select=(names(data)>=1950 & names(data)<=1970))
>
> but that doesn't work.
>
> Any ideas?
>
>
The subset() function and in particular its select argument is playing tricks with the evaluation rules, mostly to be helpful, but sometimes apparently not...

Ordinary indexing should work:

data[, names(data) >= "1950" & names(data) <= "1970"]

(using quoted strings to emphasize that you are really comparing alphabetically. That is probably OK here, but beware that

 > "999" > 1999
[1] TRUE Also, BTW, check that names really are "1950", not "X1950" or so. Data frame methods like to rationalize column names to be valid variable names.)

> Thanks! Mark
>
> [[alternative HTML version deleted]]
>
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-- 
   O__  ---- Peter Dalgaard             ุster 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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Received on Wed 26 Mar 2008 - 02:51:30 GMT

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