[R] automating merging operations from multiple dataframes

[Vladimir Eremeev]

Consider sapply and get.

There might be something like the following (untested)

fn<-function(l){  # l is supposed to be a letter. Errors will occur
otherwise.

#constructing names
  dfr.name<-paste(toupper(l),"INDSLIM",sep="")
  column.name<-paste(tolower(l),"region",sep="")

#retrieving data from the environment
  this.reg<-get(dfr.name)[,c("pid",column.name)]

#merging data frames.
#please, note "<<-". This assigns the value to the variable in this function
environment's parent frame
  PidRegion<<-merge(PidRegion,this.reg,by="pid",all=TRUE) 

# this should help avoiding too much output
  invisible(PidRegion)

}

PidRegion <- data.frame(pid=XWAVEID$pid)
sapply(letters[1:14],FUN=fn)



Jon Minton wrote:
> 
> Hi,
> 
> I have a set of dataframes names AINDSLIM, BINDSLIM, CINDSLIM ... NINDSLIM
> In each dataframe I want to extract two variables, “pid” and “{w}region”,
> where {w} means “a”, “b”, “c”, ...”n”
> At the moment my code looks like:
>> PidRegion <- data.frame(pid=XWAVEID$pid)
>> this.region <- AINDSLIM[,c("pid", "aregion")]
>> PidRegion <- merge(PidRegion, this.region, by="pid", all=T)
>> this.region <- BINDSLIM[,c("pid", "bregion")]
>> PidRegion <- merge(PidRegion, this.region, by="pid", all=T)
>> this.region <- CINDSLIM[,c("pid", "cregion")]
> ...
>> this.region <- NINDSLIM[,c("pid", "nregion")]
>> PidRegion <- merge(PidRegion, this.region, by="pid", all=T)
> 
> But surely there’s a way to automate this? 
> 
> Any suggestions?
> Jon Minton
> 

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