Shiny : variable height of renderplot - r

Question

I would like to take the height of my plot reactive because sometimes I have to draw just one graph and sometimes two or three graphs. Here my code :
output$myplot<-renderPlot({
plot_to_draw <- data[data$code==input$code,"River_name"]
plot(plot_to_draw)
number_of_plot <- length(plot_to_draw)
},height = 500*number_of_plot)
But shiny reads the height of the plot just one time so that it's not reactive.
Thank you for your answers !

Answer 1

I finally figuerd out a solution ;
server.R
output$myplot<-renderPlot({
plot_to_draw <- data[data$code==input$code,"River_name"]
plot(plot_to_draw)
number_of_plot <- length(plot_to_draw)
},height = function(){500*number_of_plot})
ui.R
plotOutput(outputId="myplot",height = "auto")

Answer 2

This is the solution that I finally got, after drudging with my app and thanks to all persons in this thread for your kind suggestions. Please don't mind the name of the variables.
In the server part:
#I had to transform my imput into a data.frame, otherwise sqldf didn't work.
country12<- reactive({as.data.frame(matrix(c(input$sel_country121),1,1))})
question12<-reactive({
country121 <- country12()
sqldf("SELECT dp.Year, dp.Type_of_Product COUNT (*) as num_products12 FROM dataPanelV5 dp, country121 p WHERE dp.Country_name = p.V1 GROUP BY dp.Year, dp.Type_of_Product")})
#I use this function to calculate the number of different types of products resulting from the query, using unique() and calculating its length, as that number is the number of facets.
n_facets12<-function(){
question121<- question12()
return (500*length(unique(question121$Type_of_Product)))}
output$barplot12 <- renderPlot({
question121<-question12()
ggplot(question121,aes(x=factor(Year),y=num_products12,fill=Type_of_Product)) + geom_bar(stat="identity") + facet_grid(Type_of_Product ~ .,scales = "free_y") +
geom_text(aes(label=num_products12), vjust=-0.2, colour="black") + scale_x_discrete(breaks=question121$Year,labels=as.character(question121$Year),position = "top") + theme(legend.position="top",axis.title.y=element_blank(),axis.text.y = element_blank(),panel.grid.major.y = element_blank(),panel.grid.minor.y = element_blank()) + labs(fill="Type_of_Product", x="Year")
},height = n_facets12)
#And it works!!