Shiny: Conditional Panel and Conditional List of checkboxGroupInput - r

Question

I want to create a shiny app for plotting the most recent pollstR charts of US presidential primaries. Users should be able to select a Party (Dem or Rep), the Candidates and the states, where the primaries (or Caucusus) took place.
I have three problems:
Based on the selected party (Dem or Rep), users should get the next checkboxGroupInput, where only the Democratic or Republican candidates appear. I try to solved that with a conditionalPanel. However, I cannot use "Candidate" twice as a name for the Widget (later in the server.R I need input$Candidate). How can I solve that?
Based on the selected party (again Dem or Rep), users should get a list of all states, where primaries and caucusus took place up to now. At the moment, I am listing all US states, which I defined before (and hence I get errors, if I want to plot the results of states, where no polls are available). Is there a way to get the list of states from the dataset, which is generated in the server.R part (it is called polls$state there, but I cannot use it, because the ui.R does not now "polls").
I plot the results as bar-charts with ggplot and the facet_wrap function (with two columns). The more states I choose, the smaller the plots get. Is there a way to set the height of the plots and insert a vertical scrollbar in the main panel?
Here is the code for the UI:
shinyUI(fluidPage(
titlePanel("2016 Presidential primaries"),
sidebarLayout(position = "right",
sidebarPanel(
helpText("Choose between Democratic (Dem) and Republican (Rep)
Primaries and Caucuses:"),
selectInput("party",
label = "Dem or Rep?",
choices = c("Dem", "Rep",
selected = "Dem")),
conditionalPanel(
condition = "input.party == 'Dem'",
checkboxGroupInput("Candidate", label = h4("Democratic Candidates"),
choices = list("Clinton" = "Clinton", "Sanders" = "Sanders"),
selected = NULL)),
conditionalPanel(
condition = "input.party == 'Rep'",
checkboxGroupInput("Candidate", label = h4("Republican Candidates"),
choices = list("Bush" = "Bush", "Carson" = "Carson", "Christie" = "Christie",
"Cruz" = "Cruz", "Kasich" = "Kasich", "Rubio" = "Rubio",
"Trump" = "Trump"),
selected = NULL)),
checkboxGroupInput("state",
label = "Select State",
choices = states,
inline = TRUE,
selected = NULL)
),
mainPanel(
tabsetPanel(
tabPanel("Plot", plotOutput("plot")),
tabPanel("Table", tableOutput("table"))
)
)
)
))
And here the code for the server.R:
### getting and cleaning the data for the shiny app-----------------------------
# load pollstR-package to get Huffpost opinion polls
require(pollstR)
# load dplyr and tidyr for data wrangling
require(dplyr)
require(tidyr)
# load ggplot2 for plotting
require(ggplot2)
# download 2016 GOP presidential primaries
repPoll <- pollstr_charts(topic='2016-president-gop-primary', showall = TRUE)
# extract and combine columns needed
choice <- repPoll$estimates$choice
value <- repPoll$estimates$value
election <- repPoll$estimates$slug
party <- repPoll$estimates$party
rep.df <- data_frame(election, choice, value, party)
# extract and combine slug and state info to add list of US state abbreviations
election <- repPoll$charts$slug
state <- repPoll$charts$state
r.stateAbb <- data_frame(election, state)
# join both data frames based on slug
rep.df <- left_join(rep.df, r.stateAbb, by = "election")
## download 2016 DEM presidential primaries
demPoll <- pollstr_charts(topic='2016-president-dem-primary', showall = TRUE)
# extract and combine columns needed
choice <- demPoll$estimates$choice
value <- demPoll$estimates$value
election <- demPoll$estimates$slug
party <- demPoll$estimates$party
dem.df <- data_frame(election, choice, value, party)
# extract and combine slug and state info to add list of US state abbreviations
election <- demPoll$charts$slug
state <- demPoll$charts$state
d.stateAbb <- data_frame(election, state)
# join both data frames based on slug
dem.df <- left_join(dem.df, d.stateAbb, by = "election")
# combine dem and rep datasets
polls <- bind_rows(dem.df, rep.df)
polls$party <- as.factor(polls$party)
polls$state <- as.factor(polls$state)
polls$choice <- as.factor(polls$choice)
shinyServer(function(input, output) {
df <- reactive({
polls %>% filter(party %in% input$party) %>% filter(choice %in% input$Candidate) %>%
filter(state %in% input$state)
})
# generate figures
output$plot <- renderPlot({
validate(
need(input$party, "Please select a party"),
need(input$Candidate, "Please choose at least one candidate"),
need(input$state, "Please select at least one state")
)
p <- ggplot(df())
p <- p + geom_bar(aes(x = choice, weight = value, fill = choice),
position = "dodge", width=.5)
# colorize bars based on parties
if (input$party == "Dem")
p <- p + scale_fill_brewer(palette = "Blues", direction = -1)
if (input$party == "Rep")
p <- p + scale_fill_brewer(palette = "Reds", direction = -1)
# add hlines for waffle-design
p <- p + geom_hline(yintercept=seq(0, 100, by = 10), col = 'white') +
geom_text(aes(label = value, x = choice, y = value + 1), position = position_dodge(width=0.9), vjust=-0.25) +
# facet display
facet_wrap( ~ state, ncol = 2) +
# scale of y-axis
ylim(0, 100) +
# delete labels of x- and y-axis
xlab("") + ylab("") +
# blank background and now grids and legend
theme(panel.grid.major.x = element_blank(), panel.grid.major.y = element_blank(),
panel.grid.minor.y = element_blank(),
panel.background = element_blank(), legend.position = "none")
print(p)
}
)
# Generate a table view of the data
output$table <- renderTable({
polls %>% filter(party %in% input$party) %>% filter(choice %in% input$Candidate) %>%
filter(state %in% input$state)
})
}
)

Answer 1

Here is the solution for problem 1 and 2:
In ui.R, replace conditionalPanel and checkboxGroupInput with
uiOutput('candidates'),
uiOutput('states')
In server.R, add the following code before df <- reactive({..... Note that you need to change some of your input$Candidate code to lower case.
observeEvent(input$party, {
output$candidates <- renderUI({
checkboxGroupInput(
"candidate",
ifelse(input$party == 'Dem', "Democratic Candidates", "Republican Candidates"),
as.vector(unique(filter(polls,party==input$party)$choice))
)
})
})
observeEvent(input$candidate, {
output$states <- renderUI({
states_list <- as.vector(unique(filter(polls, party==input$party & choice==input$candidate)$state))
checkboxGroupInput(
"state",
"Select state",
# Excluding national surveys
states_list[states_list!="US"]
)
})
})
For problem 3, change the df reactive to observe, and then set plot height depending on how many states selected. Also change this line p <- ggplot(df)
observe({
df <- polls %>% filter(party %in% input$party) %>% filter(choice %in% input$candidate) %>% filter(state %in% input$state)
height <- ceiling(length(input$state) / 2) * 200
output$plot <- renderPlot({
#Your plot code
}, height=height)
})