R help - Jul 2011 - How to translate string to variable inside a command in an easy way in R

I want to write a function that get 2 strings y and z and does the following
R command.

temp<-qq1[qq1$z==y,]
for example if it get y="AMI" and z="PrimaryConditionGroup"
It should do the following
temp<-qq1[qq1$PrimaryConditionGroup=="AMI",]

I could do it by the following function that is ugly and I wonder if there
is an easier way to do it espacielly when temp is not the final result that
I want (so I practically do not have temp<<-temp because I do not need the
function to remember temp but only to remember something else that is
calculated based on temp).

ugly<-function(y,z)
{
  text1<-paste("temp<-qq1[qq1$",z,sep="")
  text1<-paste(text1,"==y",sep="")
  text1<-paste(text1,",]",sep="")
  eval(parse(text=text1))
  temp<<-temp
}


 

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Sent from the R help mailing list archive at Nabble.com.

You are suffering from the fact that the longest distance between 2 points is a
shortcut.

The df$column notation is a shortcut for df[[column]] that has some nice
properties, but the shortcut gets in the way when you want to do something more
structured.  Try qq1[[z]]==y and avoid all that pasting, parsing, and
evaluating.

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of UriB
> Sent: Tuesday, July 05, 2011 4:30 AM
> To: r-help at r-project.org
> Subject: [R] How to translate string to variable inside a command in an
> easy way in R
> 
> I want to write a function that get 2 strings y and z and does the
> following
> R command.
> 
> temp<-qq1[qq1$z==y,]
> for example if it get y="AMI" and
z="PrimaryConditionGroup"
> It should do the following
> temp<-qq1[qq1$PrimaryConditionGroup=="AMI",]
> 
> I could do it by the following function that is ugly and I wonder if
> there
> is an easier way to do it espacielly when temp is not the final result
> that
> I want (so I practically do not have temp<<-temp because I do not
need
> the
> function to remember temp but only to remember something else that is
> calculated based on temp).
> 
> ugly<-function(y,z)
> {
>   text1<-paste("temp<-qq1[qq1$",z,sep="")
>   text1<-paste(text1,"==y",sep="")
>   text1<-paste(text1,",]",sep="")
>   eval(parse(text=text1))
>   temp<<-temp
> }
> 
> 
> 
> 
> --
> View this message in context: http://r.789695.n4.nabble.com/How-to-
> translate-string-to-variable-inside-a-command-in-an-easy-way-in-R-
> tp3645594p3645594.html
> Sent from the R help mailing list archive at Nabble.com.
> 
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