Unable to use reactive element in my shiny app - r

Question

In my shiny app,I want to change the ggplot barChart that I wish to construct. selectinput should allow to change the month (see dataset below) and so my plot should change accordingly.
problem: The isssue is, i am unable to use my reactive function or even just simple input$monthid within ggplot function.
Dataset:
Month Orders
1 Feb 984524
2 Jan 1151303
3 Mar 575000
> dput(b)
structure(list(Month = c("Feb", "Jan", "Mar"), Orders = c(984524L,
1151303L, 575000L)), .Names = c("Month", "Orders"), class = "data.frame", row.names = c(NA,
-3L))
ui.R
library(shiny)
library(shinythemes)
b<-read.csv("b.csv",header=TRUE,sep=",",stringsAsFactors=TRUE)
shinyUI(fluidPage(theme= shinytheme("flatly"),
sidebarLayout(
sidebarPanel(
selectInput(inputId = "monthid", label = "Month",choices = b$Month,selected = b$Month[1])),
mainPanel(plotOutput("plot"))
))
)
server.R
library(shiny)
library(shinythemes)
library(ggplot2)
b<-read.csv("b.csv",header=TRUE,sep=",",stringsAsFactors=TRUE)
shinyServer(function(input, output) {
#making a reactive object
m<-reactive ({
as.character(input$monthid)
})
output$plot<- renderPlot({
#probably I am making a subset error in x inside aes parameter
ggplot(data = b, aes(x = b[,m()] ,y = b$Orders)) + geom_bar(stat="identity")
})
})

Answer 1

Here's a minimal working example you can copy and paste right in your session to run, but a bar chart with a single bar doesn't really make a lot of sense (and looks ugly if you ask me):
library(shiny)
shinyApp(
ui = fluidPage(
sidebarLayout(
sidebarPanel(
selectInput(
inputId = "monthid",
label = "Month",
choices = b$Month,
selected = b$Month[1]
)
),
mainPanel(plotOutput("plot"))
)
),
server = function(input, output) {
DF <- reactive({
b[b$Month == input$monthid, , drop = FALSE]
})
output$plot <- renderPlot({
ggplot(DF(), aes(x = Month, y = Orders)) +
geom_bar(stat = "identity")
})
}
)
It looks somewhat like this:
Since that doesn't look nice IMO, you could do something with highlighting the currently selected bar, for example:
b$highlight <- factor("Not Selected", levels = c("Not selected", "Selected"))
shinyApp(
ui = fluidPage(
sidebarLayout(
sidebarPanel(
selectInput(
inputId = "monthid",
label = "Month",
choices = b$Month,
selected = b$Month[1]
)
),
mainPanel(plotOutput("plot"))
)
),
server = function(input, output) {
DF <- reactive({
b[b$Month == input$monthid, "highlight"] <- "Selected"
b
})
output$plot <- renderPlot({
ggplot(DF(), aes(x = Month, y = Orders, fill = highlight)) +
geom_bar(stat = "identity")
})
}
)
This would look as follows: