Why RenderPlot does not produce any graph in shiny app?

Question

I am learning to make my first shiny app about a simulation. I tried to make a network graph in shiny with pre-written code, but no graph appeared when I run the app. I am not sure what did I miss and would really appreciate it if someone can point it out. Thanks!

here's my code for the ui.R.

library(shiny)
library(shinythemes)
library(shinydashboard)
library(igraph)

# Define UI
ui <- fluidPage(
  theme = shinytheme("flatly"),
  navbarPage(
    "Can't I just go to one party?",
    tabPanel(
      "Network Graph",
      sidebarPanel(
        sliderInput(
          "n.people",
          "Number of people who lived near campus:",
          min = 1,
          max = 1000,
          value = 500
        ),
        
        sliderInput(
          "n.workers",
          "Number of people have in-person jobs:",
          min = 1,
          max = 10,
          value = 5
        ),
        sliderInput(
          "n.roommates",
          "Number of rommates to live with:",
          min = 1,
          max = 10,
          value = 5
        ),
        plotOutput("hist")
      ),
      
      # sidebarPanel
      mainPanel(
        h1("Network Simulation"),
        h4("How connected are we?"),
        verbatimTextOutput("txtout"),
        
      ) # mainPanel
      
    )
  ) # navbarPage) # fluidPage
)

and here's my code for the server.R

# Define server function
server <- function(input, output) {
        output$hist <- renderPlot({
                distribution <- matrix(0, input$n.people, input$n.people)
                ### Set up the coworker connections
                # 50% of people randomly selected to be workers
                workers <- sample(
                        1:input$n.people,
                        size = 0.5 * input$n.people,
                        replace = FALSE
                )
                # For each worker, randomly select 2 coworkers.
                for (w in workers) {
                        while (sum(distribution[w,]) < input$n.workers + 1) {
                                availableWorkers <-
                                        workers[rowSums(distribution[workers,]) < input$n.workers]
                                if (length(availableWorkers[which(availableWorkers != w)]) > input$n.workers -
                                    1) {
                                        c <- sample(availableWorkers[which(availableWorkers != w)],
                                                    size = 1,
                                                    replace = FALSE)
                                }
                                if (length(availableWorkers[which(availableWorkers != w)]) == input$n.workers -
                                    1) {
                                        c <- availableWorkers[which(availableWorkers != w)]
                                }
                                if (length(availableWorkers[which(availableWorkers != w)]) == 0) {
                                        break
                                }
                                distribution[w, c] <- 1
                                distribution[c, w] <- 1
                        }
                }
                
                #Set up the roommate connection
                # Everyone has exactly 1 roommate
                # Person 1 is roommates with person i+1
                
                for (i in 1:(input$n.people - input$n.roommates)) {
                        for (j in 1:input$n.roommates) {
                                distribution[i, i + j] <- 1
                                distribution[i + j, i] <- 1
                        }
                }
                
                ### Everone either has 3 edges or 1 edge
                ### Workers have 3, nonworkers have 1
                distribution_graph <-
                        graph_from_adjacency_matrix(distribution, "undirected")
                plot(distribution_graph)
                
        })
        
}

and my code for the shiny app itself

#loading the necessary libraries and packages
library(shiny)
library(plotly)
library(dplyr)
library(ggplot2)
source("ui.R")
source("server.R")

# Calling the other files
shinyApp(ui = ui, server = server)

Answer 1

I tested the app with smaller default values of your inputs ( n.people = 50, n.workers = 3, n.roommates = 3) and this works fine. When I increase the values using the sliders, at some point the app does not react anymore. There is no clear breakpoint: sometimes it works with a given parameter setting, and the next time it stops, which is probably due to the sampling process. So, it seems that what you are doing is just too memory-heavy for R.

There is certainly a limit to matrix dimensions, and if this is the problem, than you cannot really do anything about it. But maybe you can re-write your loops such that they need less memory?, I recommend doing the testing outside the shiny app. because shiny itself is not the problem here.