plots that flow??

reflowPlotOutput.R

library(shiny)

# example data
df <-
  as.data.frame(matrix(rnorm(250), nrow=25)) %>%
  rownames_to_column(var = "Year") %>%
  mutate(Year = as.numeric(Year))

# Define UI for application that draws a histogram
ui <- fluidPage(
  fluidRow(
    column(width=8, selectInput('chart_list', 'Variables to plot', choices = names(df), multiple = T, width='100%')),
    column(width=4, sliderInput('chart_height', 'Chart height', 100, 1000, 500))
  ),
  uiOutput('plots')
)

# Define server logic required to draw a histogram
server <- function(input, output) {
  
  rv <- reactiveValues()
  
  # when the selected variables change:
  observeEvent(input$chart_list, {
    
    req(input$chart_list)
    rv$n_plots <- length(input$chart_list)
    
    for(i in 1:rv$n_plots){
      
      local({
        ii <- i
        # get each plot and save to output list
        plotname <- paste("plot", ii, sep="")
        output[[plotname]] <- renderPlot({
          ggplot(df, aes_string("Year", input$chart_list[ii])) +
            geom_line() +
            ggtitle(input$chart_list[ii])
        })
      })
      
    }

  })
  
  output$plots <- renderUI({
    req(rv$n_plots)
    
    if(rv$n_plots == 1){
      # just do a normal plotOutput for the selected plot
      plotname <- paste("plot", 1, sep="")
      plotOutput(plotname, height = paste(input$chart_height, "px", sep=''))
      
    } else if(rv$n_plots > 1){
      # split the number of plots in two, create two columns and put in a fluidRow.
      
      # get list of objects in each column (First col is 1, 3, 5, etc. Second is 2, 4, 6, etc.)
      plot_output_list1 <- lapply(seq(1, rv$n_plots, by=2), function(ii) {
        plotname <- paste("plot", ii, sep="")
        plotOutput(plotname, height = paste(input$chart_height, "px", sep=''))
      })
      plot_output_list2 <- lapply(seq(2, rv$n_plots, by=2), function(ii) {
        plotname <- paste("plot", ii, sep="")
        plotOutput(plotname, height = paste(input$chart_height, "px", sep=''))
      })
      
      # get breaks for each plot in the lists
      plot_output_list_break1 <- rep(list(br()), length(plot_output_list1))
      plot_output_list_break2 <- rep(list(br()), length(plot_output_list2))
      
      # get the combined list of plots and breaks by interleaving the lists
      plot_output_list1 <- c(rbind(plot_output_list1, plot_output_list_break1))
      plot_output_list2 <- c(rbind(plot_output_list2, plot_output_list_break2))
      
      # plot the charts in their respective columns
      fluidRow(
        column(width=6, do.call(tagList, plot_output_list1)),
        column(width=6, do.call(tagList, plot_output_list2))
      )
      
    }
    
  })
}

# Run the application 
shinyApp(ui = ui, server = server)