Excel VBA and R: batch mode vs interactive mode

Question

I am able to execute R in batch mode via Excel VBA with the code below, but this method limits interactivity because R closes after completion of the script. I would like to be able to make further calls to R based on Excel user input, while utilizing the R objects created in the first call. Is there a way to keep R active while still utilizing VBA to send messages to R?

Sub Run_R()

Dim shell As Object, Rcmd As String, retval As Variant

Set shell = VBA.CreateObject("WScript.Shell")
Rcmd = "Rscript C:\test.R"
retval = shell.Run(Rcmd, 0, True)

End Sub

Answer 1

Consider segmenting the two processes. Have Excel VBA obtain all needed user-input values through spreadsheet or userform, and then pass them into R script. R reads such values as command line args for a longer routine of operations.

Here, R is spawned as a child process in your application akin to aa separate macro or function which receives input parameters and processes an output:

VBA

Sub Run_R()

    Dim shell As Object, Rcmd As String, retval As Variant
    Dim var1, var2 As Double

    var1 = Range("A2").Value
    var2 = Range("A5").Value

    Set shell = VBA.CreateObject("WScript.Shell")
    Rcmd = "Rscript C:\test.R " & var1 & " " & var2
    retval = shell.Run(Rcmd, 0, True)

End Sub

R

args <- commandArgs(trailingOnly=T)

var1 <- args[1]
var2 <- args[2]

# ... run other operations ...