On Apr 30, 2013, at 6:00 AM, arun wrote:
> Hi,
> May be this helps:
> funcName<- function(df1, x){
> whatCol=df1[[x]]
> print("Got it")
> print(whatCol)
> }
>
> funcName(df,"ColA")
> #[1] "Got it"
> #[1] 1 2 3 4 5
> funcName(df,"ColB")
> #[1] "Got it"
> #[1] A B C D E
> #Levels: A B C D E
>
>
To ST;
You should now realize that this function has already been built into R and its
name is "[[".
The "$" function is just variation on "[[" that does not evaluate its argument.
You effort to parse back to paste("df",x,sep="$") failed, but might have
succeeded if you took this route:
eval(parse(text= paste("df",x,sep="$") ) )
I'm not saying you should have done that since obviously "[[" is the proper,
approved, economical way to do it. I'm just trying to get you to understand the
language better. You should spend further time with:
help("Extract") # to cement this lesson and extend your understanding.
--
David.
> A.K.
>
>
>> I am trying to extract the 2nd column from a dataframe using a function
> called funcName. Note this is an example that I need cos I am using it
> to >read the values I pass into a function call - these passed values
> represent dataframe column names. I am trying to use this concept for a
> vary large >dataframe with 100+ columns.
>>
>> ColA <- c(1,2,3,4,5)
>> ColB <- c("A","B","C","D","E")
>> df <- data.frame(ColA,ColB)
>>
>> funcName <- function(x) {
>> whatCol = paste("df",x,sep="$")
> >print("Got it",whatCol)
>> }
>>
>> funcName("ColA")
>>
>> Please advise, since this code is not working. Thanks in advance.
>>
>> -ST
>
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius
Alameda, CA, USA
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