R help - Sep 2011 - Passing in Condtions into Object

Hello,

I am trying to pass a conditional expression into an expression to be
evaluated when ever an R statement is called.  For example:

get_unique_count <- function(df, select, field){
   uniqs <- unique(subset(df, select)[field])
   return (nrow(uniqs))
}


In this case select is a conditional statement year == 1980, and the
function would be called in the following manner:

library(ggplot2)
get_unique_count(mpg, year==1980, 'manufacturer')

Thank for any help in advance,

-- Adam

On Sep 8, 2011, at 8:21 PM, Adam Pridgen wrote:
> Hello,
>
> I am trying to pass a conditional expression into an expression to be
> evaluated when ever an R statement is called.  For example:
>
> get_unique_count <- function(df, select, field){
>   uniqs <- unique(subset(df, select)[field])
>   return (nrow(uniqs))
> }
>
>
> In this case select is a conditional statement year == 1980, and the
> function would be called in the following manner:
>
> library(ggplot2)
> get_unique_count(mpg, year==1980, 'manufacturer')
Borrowing heavily from subset.data.frame:

get.uniq <- function (x, logic.expr, field)
{
     e <- substitute(logic.expr)
     r <- eval(e, x, parent.frame())
         if (!is.logical(r))
             stop("'subset' must evaluate to logical")
         r <- r & !is.na(r)
     if (missing(field))
         vars <- TRUE
     else {
         nl <- as.list(seq_along(x))
         names(nl) <- names(x)
         vars <- eval(substitute(field), nl, parent.frame())
     }
     uniqs <- unique(x[r, field, drop = FALSE])
    NROW(uniqs)
}
>
> Thank for any help in advance,
>
> -- Adam
>
> ______________________________________________
> 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.
David Winsemius, MD
Heritage Laboratories
West Hartford, CT

Would:

tapply(mpg,list(year,manufacturer), function(x) length(unique(x)))

do what you are trying to accomplish? Or do you need very specific subsets?
If so, you can do:

year<-c(rep(1980,4),rep(1981,4))
manufacturer<-rep(c('A','B'),4)
mpg<-sample(c(1:2),8,replace=T)

guc<-function(x,y,z){length(unique(x[year==y&manufacturer==z]))}

#apply the function: e.g.

guc(mpg,1980,'A')

HTH,
Daniel


Adam Pridgen wrote:
> 
> Hello,
> 
> I am trying to pass a conditional expression into an expression to be
> evaluated when ever an R statement is called.  For example:
> 
> get_unique_count <- function(df, select, field){
>    uniqs <- unique(subset(df, select)[field])
>    return (nrow(uniqs))
> }
> 
> 
> In this case select is a conditional statement year == 1980, and the
> function would be called in the following manner:
> 
> library(ggplot2)
> get_unique_count(mpg, year==1980, 'manufacturer')
> 
> Thank for any help in advance,
> 
> -- Adam
> 
> ______________________________________________
> 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.
> 
--
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