Problems using ggvis in rMarkdown with variables - r-markdown

Question

Hi having a couple of problems
a) creating the correct text to pass variables to ggvis - not even sure aes_string is applicable
b) The plot propagates in browser rather than rendering in the rmarkdown document
Here is an example
---
title: "Untitled"
author: "pssguy"
date: "Sunday, August 24, 2014"
output: html_document
runtime: shiny
---
```{r, echo = FALSE, message=FALSE}
library(ggplot2)
library(ggvis)
library(dplyr)
selectInput("category3", "Choose Dataset:", c("mpg", "disp", "qsec"))
# ggplot renders correctly within renderPlot
renderPlot({
ggplot(mtcars,aes_string(input$category3,"disp"))+geom_point()
})
# ggvis works within document with hard coded info
mtcars %>% ggvis(~wt,~disp)
mtcars %>% ggvis(aes_string(paste("~",input$category3,","),"~disp"))
#Operation not allowed without an active reactive context. (You tried to do something that can only be done from inside a reactive expression or observer.)
# This needs correcting anyways
renderPlot({
mtcars %>% ggvis(aes_string(paste("~",input$category3,","),"~disp"))
})
# <text>:1:7: unexpected ',' 1: ~ mpg ,
# even if the above is corrected the plot opens in a browser rather than the document
renderPlot({
mtcars %>% ggvis(~wt,~disp)
})
```
TIA

Answer 1

This should do it:
---
title: "Untitled"
output: html_document
runtime: shiny
---
```{r, echo = FALSE, message=FALSE}
library(ggplot2)
library(ggvis)
library(dplyr)
selectInput("category3", "Choose Dataset:", c("mpg", "disp", "qsec"))
# ggplot renders correctly within renderPlot
renderPlot({
print(input$category3)
ggplot(mtcars,aes_string(input$category3,"disp"))+geom_point()
})
# ggvis with dynamically changing columns
reactive({
if (!is.null(input$category3))
col <- input$category3
else
col <- "mpg"
mtcars %>% ggvis(prop("x", as.name(col)), ~disp)
}) %>% bind_shiny('foo')
ggvisOutput('foo')
```
It's a little complicated because you need a NULL check for the category, and you need to explicitly tell knitr to put a ggvis output on the page.