Interactive model

server.R

library(shiny)

shinyServer(function(input, output) {
    model <- reactive({
        brushed_data <- brushedPoints(trees, input$brush1, xvar = "Girth", yvar = "Volume")
        if (nrow(brushed_data) < 2) {
            return(NULL)
        }
        lm(Volume ~ Girth, data = brushed_data)
    })
    
    output$slopeOut <- renderText({
        if (is.null(model())) {
            "No Model Found"
        } else {
            model()[[1]][2]
        }
    })
    
    output$intOut <- renderText({
        if (is.null(model())) {
            "No Model Found"
        } else {
            model()[[1]][1]
        }
    })
    
    output$plot1 <- renderPlot({
        plot(trees$Girth, trees$Volume, xlab = "Girth",
             ylab = "Volume", main = "Tree Measurements",
             cex = 1.5, pch = 16, bty = "n")
        if (!is.null(model())) {
            abline(model(), col = "blue", lwd = 2)
        }
    })    
})

ui.R

library(shiny)

shinyUI(fluidPage(
    titlePanel("Visualize Many Models"),
    sidebarLayout(
        sidebarPanel(
            h3("Slope"),
            textOutput("slopeOut"),
            h3("Intercept"),
            textOutput("intOut")
        ),
        mainPanel(
            plotOutput("plot1", brush = brushOpts(
                id = "brush1"
            ))
        )
    )
))