global.R

obesity = read.csv(
  'http://www.stat.berkeley.edu/classes/s133/data/obesity.csv',
  stringsAsFactors = F
)
names(obesity) = gsub("\\.", "_", names(obesity))
# add column with two letter state names and 
obesity = plyr::mutate(obesity, 
  State = stringr::str_trim(State),
  state = state.abb[match(State, state.name)],
)

server.R

library(shiny)
library(rMaps)

shinyServer(function(input, output, session){
  output$mychoro = renderChart2({
    choropleth(
      cut(Adult_Obesity_Rate, 5, labels = F) ~ state,
      data = obesity,
      pal = input$mypal
    )
  })
})

ui.R

library(shiny)
library(rMaps)
shinyUI(pageWithSidebar(
  headerPanel('Datamaps with Shiny'),
  sidebarPanel(
    selectInput('mypal', 'Palette', c('PuRd', 'Blues'))
  ),
  mainPanel(
    chartOutput('mychoro', 'datamaps')  
  )
))