Using as.name in ddply .(variable) results in an error "object 'grp' not found"

getMinMax_with_without_as.name.r

## Doesn't work 

# grp -- name of a column of the the data.frame df
# function call is -- getMinMax1( df1 , grp = "g10")

getMinMax1 <-function(df, grp){
      dfret <- ddply( df , .(as.name(grp)), ## I am using as.name(grp), source of error
            function(x){
                minmax <- c(mix(x[ , 3]), max(x[ ,3]))
                return(minmax)
            }
            )
      return(dfret)
  }

## Works fine
# grp -- name of a column of the the data.frame df
# function call is -- getMinMax2( df1 , grp = "g10")

getMinMax2 <-function(df, grp){
      dfret <- ddply( df , grp, ## using the quoted variable name passed to grp when the fun is called
            function(x){
                minmax <- c(min(x[ , 3]), max(x[ ,3]))
                return(minmax)
            }
            )
      return(dfret)
  }