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I'm trying to create a Shiny app to create a scatterplot based on the Iris data set. The code generates the app, but displays only a single point on the graph, no matter what settings I choose in the app. Here's the code:

options(warn = -1)
library(shiny)
library(shinythemes)
library(dplyr)
library(readr)
library(ggplot2)
options(warn=0)



# Define UI
ui <- fluidPage(theme = shinytheme("superhero"),
 titlePanel("Iris"),
 sidebarLayout(
 sidebarPanel(

 # Select Inputs
 selectInput(inputId = "y",
 label = "Y-axis:",
 choices = c("Sepal.Length", "Sepal.Width", "Petal.Length", "Petal.Width"),
 selected = "Sepal.Length"),

 selectInput(inputId = "x",
 label = "X-axis:",
 choices = c("Sepal.Length", "Sepal.Width", "Petal.Length", "Petal.Width"),
 selected = "Petal.Length")
 ),

 # Output
 mainPanel(
 plotOutput(outputId = "scatterplot")
 )
 )
)

# Define server function
server <- function(input, output) 

 # Create the scatterplot object the plotOutput function is expecting
 output$scatterplot <- renderPlot(
 ggplot(data = iris, aes(x = input$x, y = input$y))+
 geom_point(aes(color=Species, shape=Species))+
 geom_smooth(method="lm")
 )


shinyApp(ui=ui, server=server)

it's because your input$x is actually a string. So replace aes() with aes_string() in your ggplot call:

library(ggplot2)

# This doesn't work: aes
ggplot(data = iris, aes(x = "Sepal.Length", y = "Sepal.Width"))+
 geom_point(aes(color=Species, shape=Species))+
 geom_smooth(method="lm")

# This works : aes_string
ggplot(data = iris, aes_string(x = "Sepal.Length", y = "Sepal.Width"))+
 geom_point(aes(color=Species, shape=Species))+
 geom_smooth(method="lm")

See: passing string to ggplot function