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

[Peter Dalgaard]

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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>   


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