Error with dates and reactive inputs in R Shiny - r

Question

I am putting together a small R Shiny app which will take several inputs from the user and use these inputs to subset a data frame and provide back two histograms. The users will pick a baseball season, two teams and then this information will provide a reactive list of possible games played between these two teams. The user will then pick a date/game and then a histogram will be displayed for each team which will show the distribution of runs scored per game for each team for all games within that season up to the date/game selected. I feel like I am almost there, I just need to get this date thing sorted out. Right now with the code as is, everything evaluates but I get this error twice;
Warning: Error in eval: do not know how to convert 'input$dates' to class “Date”
and this error twice;
Warning in eval(substitute(expr), envir, enclos) :
Incompatible methods ("Ops.factor", "Ops.Date") for "<"
ui.R
library(shiny)
library(dplyr)
shinyUI(fluidPage(
# Application title
titlePanel("Predicting the winner of a Major League Baseball game"),
sidebarLayout(
sidebarPanel(
selectInput("season","1. Select an MLB Season",
choices = list(2012,2013,2014,2015),
selected = 2012),
selectInput("var_1","2. Select the first team",
choices = c("ARI","ATL","BAL","BOS","CHC","CHW","CIN","CLE","COL","DET",
"HOU","KCR","LAA","LAD","MIA","MIL","MIN","NYM","NYY","OAK",
"PHI","PIT","SDP","SFG","SEA","STL","TBR","TEX","TOR","WSN"),
selected = "BAL"),
selectInput("var_2","3. Select the second team",
choices = c("ARI","ATL","BAL","BOS","CHC","CHW","CIN","CLE","COL","DET",
"HOU","KCR","LAA","LAD","MIA","MIL","MIN","NYM","NYY","OAK",
"PHI","PIT","SDP","SFG","SEA","STL","TBR","TEX","TOR","WSN"),
selected = "BOS"),
uiOutput("dates"),
sliderInput("bins",
"Binwidth:",
min = 1,
max = 5,
value = 2)
),
#main panel
mainPanel(
plotOutput("first_team_hist"),
plotOutput("second_team_hist")
)
)))
server.R
library(shiny)
library(dplyr)
library(ggplot2)
shinyServer(
function(input, output) {
mydf <- read.csv("batting_game_logs_merged.csv")
inputData_1 <- reactive({
filter(mydf,team == input$var_1 & season == input$season & date < as.Date(input$dates,format = "%Y-%m-%d"))
})
inputData_2 <- reactive({
filter(mydf,team == input$var_2 & season == input$season & date < as.Date(input$dates,format = "%Y-%m-%d"))
})
output$dates <- renderUI({
dates = mydf %>% filter(team == input$var_1 & opponent_team == input$var_2 & season == input$season) %>% select(date)
selectInput("dates","Pick a Game Date", as.character(dates[[1]]))
})
output$first_team_hist <- renderPlot({
myplot_1 <- ggplot(inputData_1(), aes(x = team_batting_gamelogs.R)) +
geom_histogram(aes(y = ..density..),
binwidth = input$bins, fill = I("blue"),col = I("red")) +
labs(title = paste("Runs Scored per game for",input$var_1),
x= "Runs Scored per Game", y = "Density")
print(myplot_1)
})
output$second_team_hist<- renderPlot({
myplot_2 <- ggplot(inputData_2(), aes(x = team_batting_gamelogs.R)) +
geom_histogram(aes(y = ..density..),
binwidth = input$bins, fill = I("blue"),col = I("red")) +
labs(title = paste("Runs Scored per game for",input$var_2),
x= "Runs Scored per Game", y = "Density")
print(myplot_2)
})
}
)
Thank you in advance for taking the time to review my problem.
-Josh

Answer 1

I am guessing your problem is the initial NULL value of your input$dates. Your reactive environments inputData_1/2 respond as soon as your UI is rendered (and they get their selected value). But no value has been assigned to input$dates yet, so your first run of these functions gets a NULL. Confirm that as.Date(NULL) yields exactly your error.
I advice you to make your reactive environments only listen to input$dates, i.e.
inputData_1 <- eventReactive(input$dates, {
filter(mydf,team == input$var_1 & season == input$season & date < as.Date(input$dates,format = "%Y-%m-%d"))
})
inputData_2 <- eventReactive(input$dates, {
filter(mydf,team == input$var_2 & season == input$season & date < as.Date(input$dates,format = "%Y-%m-%d"))
})
As far as I can see, you want computations to start only after inserting a date anyway.
Other possible fixes are to isolate the other variables or just add an if(!is.null(input$dates)){ ... } clause to handle NULL input.