R help - Feb 2010 - Access variables by string

Dear all,

I have two probably very easy questions:

(1) Is there a way to access certain variables by their string-based 
name representation?

Example:
numbers <- c("one", "two", "three")
varname <- "numbers"
print(varname[2])

(2) I need this functionality for a customized na.exclude() function 
that I am building, which should only exclude rows that have NA in 
certain columns. Maybe there is already a function which does 
exactly what I need, so I'd highly appreciate if someone could point 
me there ;)

My current implementation looks like this:

naexlcude <- function(data, varnames)
{
	for(v in varnames){
		data = subset(data, !is.na(v))
	}

	data
}

Best
Philipp

On Thu, Feb 11, 2010 at 4:18 PM, Philipp Rappold
<philipp.rappold at gmail.com> wrote:
> Dear all,
>
> I have two probably very easy questions:
>
> (1) Is there a way to access certain variables by their string-based name
> representation?
>
> Example:
> numbers <- c("one", "two", "three")
> varname <- "numbers"
> print(varname[2])
print(get(varname)[2])
>
> (2) I need this functionality for a customized na.exclude() function that I
> am building, which should only exclude rows that have NA in certain
columns.
> Maybe there is already a function which does exactly what I need, so
I'd
> highly appreciate if someone could point me there ;)
>
> My current implementation looks like this:
>
> naexlcude <- function(data, varnames)
> {
> ? ? ? ?for(v in varnames){
> ? ? ? ? ? ? ? ?data = subset(data, !is.na(v))
> ? ? ? ?}
>
> ? ? ? ?data
> }
f = function(x, vars) x[complete.cases(x[vars]),]

b
>
> Best
> Philipp
>
> ______________________________________________
> R-help at r-project.org 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.
>

Philipp Rappold wrote:
> Dear all,
> 
> I have two probably very easy questions:
> 
> (1) Is there a way to access certain variables by their string-based
> name representation?
> 
> Example:
> numbers <- c("one", "two", "three")
> varname <- "numbers"
> print(varname[2])
> 
> (2) I need this functionality for a customized na.exclude() function
> that I am building, which should only exclude rows that have NA in
> certain columns. Maybe there is already a function which does exactly
> what I need, so I'd highly appreciate if someone could point me there
;)
> 
> My current implementation looks like this:
> 
> naexlcude <- function(data, varnames)
> {
>     for(v in varnames){
>         data = subset(data, !is.na(v))
>     }
> 
>     data
> }
> 
Well, you can use get(varname)[2] or more generally things like
eval(bquote(.(as.name(varname))[2])), but for this particular
application, why not just use the standard indexing techniques?

I think this will do

ix <- apply(is.na(data[varnames]), 1, any)
data[!ix,]

e.g.
> table(apply(is.na(airquality[c("Wind","Ozone")]),1,
any))
FALSE  TRUE
  116    37
> colSums(is.na(airquality))
  Ozone Solar.R    Wind    Temp   Month     Day
     37       7       0       0       0       0
> table(apply(is.na(airquality[c("Solar.R","Ozone")]),1,
any))
FALSE  TRUE
  111    42


(Using functions like subset inside another function often leads to
problems because of the nonstandard evaluation tricks that it uses. It
is mainly useful to save tying on the command line.)

-- 
   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

Philipp Rappold <philipp.rappold <at> gmail.com> writes:
> 
> Dear all,
> 
[...]
> (2) I need this functionality for a customized na.exclude() function 
> that I am building, which should only exclude rows that have NA in 
> certain columns. Maybe there is already a function which does 
> exactly what I need, so I'd highly appreciate if someone could point 
> me there ;)
I would use something like

naexclude <- function(data, varnames)
    d[rowSums(is.na(data[,varnames,drop=FALSE])) == 0,]

Dan
> 
> My current implementation looks like this:
> 
> naexlcude <- function(data, varnames)
> {
> 	for(v in varnames){
> 		data = subset(data, !is.na(v))
> 	}
> 
> 	data
> }
> 
> Best
> Philipp
> 
>

For your first question, use the get() function

-Don

At 5:18 PM +0100 2/11/10, Philipp Rappold wrote:
>Dear all,
>
>I have two probably very easy questions:
>
>(1) Is there a way to access certain variables by their string-based 
>name representation?
>
>Example:
>numbers <- c("one", "two", "three")
>varname <- "numbers"
>print(varname[2])
>
>(2) I need this functionality for a customized na.exclude() function 
>that I am building, which should only exclude rows that have NA in 
>certain columns. Maybe there is already a function which does 
>exactly what I need, so I'd highly appreciate if someone could point 
>me there ;)
>
>My current implementation looks like this:
>
>naexlcude <- function(data, varnames)
>{
>	for(v in varnames){
>		data = subset(data, !is.na(v))
>	}
>
>	data
>}
>
>Best
>Philipp
>
>______________________________________________
>R-help at r-project.org 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.

-- 
--------------------------------------
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA
925-423-1062