R shiny: Error in chart$html : $ operator is invalid for atomic vectors

Question

I'm trying to write interactive piecharts using Shiny but keep getting this error

Error in chart$html : $ operator is invalid for atomic vectors

I have 3 data sets, one has the whole data set, one is how many things were passed and the other is how many failed. I've the following code:

server.R

library(shiny)
library(googleVis)

y1<-read.csv("y1.csv")
y2<-read.csv("y2.csv")
y3<-read.csv("y3.csv")

shinyServer(function(input, output) {
    datasetInput <- reactive({
      switch(input$dataset,
             "full content" = y1,
             "passed content" = y2,
             "failed content" = y3, select = "full content")
    })



 output$view <- renderGvis({
      dok <-gvisPieChart(datasetInput(), options=list(width=500, height=500))
      plot(dok)
    })
  })

ui.R

# ui.R
shinyUI(pageWithSidebar(
  headerPanel("Degree of knowledge distribution for content"),
  sidebarPanel(
    selectInput("dataset", "Choose:", 
                choices = c("full content", "passed content", "failed content"))
  ),
  mainPanel(
    htmlOutput("view")
  )
))

My y csv files are 5 observations of two variables, the name of the content and the number of them