R : How to create objects with a function which name and value depend on an argument, and that these objects are found in the global environment?

I have the following situation: I have different dataframes, I would like to be able, for each dataframe, to create 2 dataframes according to the value of one of the columns (log2FoldChange>1 and logFoldChange<-1).

For this I use the following code:

DJ29_T0_Overexpr = DJ29_T0[which(DJ29_T0$log2FoldChange > 1),]
DJ29_T0_Underexpr = DJ29_T0[which(DJ21_T0$log2FoldChange < -1),]

DJ229_T0 being one of my dataframe.

First problem: the sign for the dataframe where log2FoldChange < -1 is not taken into account.

But the main problem is at the time of making the function, I wrote the following:

spliteOverUnder <- function(res){
  nm <-deparse(substitute(res))
  assign(paste(nm,"_Overexpr", sep=""), res[which(as.numeric(as.character(res$log2FoldChange)) > 1),])
  assign(paste(nm,"_Underexpr", sep=""), res[which(as.numeric(as.character(res$log2FoldChange)) < -1),])
}

Which I then ran with :

spliteOverUnder(DJ29_T0)

No error message, but my objects are not exported in my global environment. I tried with return(paste(nm,"_Overexpr", sep="") but it only returns the object name but not the associated dataframe.

Using paste() forces the use of assign(), so I can’t do :

spliteOverUnder <- function(res){
  nm <-deparse(substitute(res))
  paste(nm,"_Overexpr", sep="") <<- res[which(as.numeric(as.character(res$log2FoldChange)) > 1),]
  paste(nm,"_Underexpr", sep="") <<- res[which(as.numeric(as.character(res$log2FoldChange)) < -1),]
}

spliteOverUnder(DJ24_T0)

I encounter the following error:

Error in paste(nm, "_Overexpr", sep = "") <<- res[which(as.numeric(as.character(res$log2FoldChange)) > : 
  could not find function "paste<-"

If you’ve encountered this difficulty before, I’d appreciate a little help.
And if you knew, once the function works, how to use a For loop going through a list containing all my dataframes to apply this function to each of them, I’m also a taker.

Thanks

>Solution :

When assigning, use the pos argument to hoist the new objects out of the function.

function(){
    assign(x = ..., value = ...,
           pos = 1 ## see below
    )
}

… where 0 = the function’s local environment, 1 = the environment next up (in which the function is defined) etc.