R help - Jan 2007 - Use a text variable's value to specify another varaible?

Greetings guRus --

 

If a variable, e.g., 'varname', is a character string, e.g. varname
<-
"datavector", and I want to apply a function, such as table(), to
datavector, what syntax or method will do so using only the variable
varname?  This seems similar to indirect addressing, but I have not seen
a method for it in the R manuals.  Is there a general name for such
indirect reference that one might search for?

 

(This came up while writing a function that takes the value of 'varname'
from the keyboard and then applies functions to it.)

 

With thanks for any solution,

 

Ben Fairbank

 


	[[alternative HTML version deleted]]

On Fri, 2007-01-26 at 09:48 -0600, Ben Fairbank wrote:
> Greetings guRus --
> If a variable, e.g., 'varname', is a character string, e.g. varname
<-
> "datavector", and I want to apply a function, such as table(), to
> datavector, what syntax or method will do so using only the variable
> varname?  This seems similar to indirect addressing, but I have not seen
> a method for it in the R manuals.  Is there a general name for such
> indirect reference that one might search for?
> (This came up while writing a function that takes the value of
'varname'
> from the keyboard and then applies functions to it.)
> With thanks for any solution,
> Ben Fairbank

See ?get and ?assign


datavector <- 1:10
varname <- "datavector"
> get(varname)
 [1]  1  2  3  4  5  6  7  8  9 10
> log10(get(varname))
 [1] 0.0000000 0.3010300 0.4771213 0.6020600 0.6989700 0.7781513
 [7] 0.8450980 0.9030900 0.9542425 1.0000000


and/or

assign(varname, letters)
> datavector
 [1] "a" "b" "c" "d" "e"
"f" "g" "h" "i" "j"
"k" "l" "m" "n" "o"
"p" "q"
[18] "r" "s" "t" "u" "v"
"w" "x" "y" "z"
> get(varname)
 [1] "a" "b" "c" "d" "e"
"f" "g" "h" "i" "j"
"k" "l" "m" "n" "o"
"p" "q"
[18] "r" "s" "t" "u" "v"
"w" "x" "y" "z"


HTH,

Marc Schwartz

Can I ask why you aren't just passing in the object to your function, 
but instead a text name for that object?

Ben Fairbank wrote:
> Greetings guRus --
> 
>  
> 
> If a variable, e.g., 'varname', is a character string, e.g. varname
<-
> "datavector", and I want to apply a function, such as table(), to
> datavector, what syntax or method will do so using only the variable
> varname?  This seems similar to indirect addressing, but I have not seen
> a method for it in the R manuals.  Is there a general name for such
> indirect reference that one might search for?
> 
>  
> 
> (This came up while writing a function that takes the value of
'varname'
> from the keyboard and then applies functions to it.)
> 
>  
> 
> With thanks for any solution,
> 
>  
> 
> Ben Fairbank
> 
>  
> 
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.