See example for the element order in the vectors :
inpboxe4.png
To get the menu, just use the following code:
vlabel<-c('matrix 1','matrix 2','matrix 3','matrix 4')inp<-c('M','N','S','R')ans<-inpboxe4(vlabel,inp)
References
Lawrence M.F.,Verzani J., (2012) Programming Graphical User Interfaces in R,CRC Press Taylor & Francis Group