title: json format to csv format conversion, using R
body: <p>I have a json file as follows:  </p>
  
  <pre><code>library(RCurl)
  library(RJSONIO)
  url &lt;- 'http://www.pm25.in/api/querys/aqi_details.json?city=shijiazhuang&amp;token=5j1znBVAsnSf5xQyNQyq'
  web &lt;- getURL(url)
  raw &lt;-fromJSON(web)
  </code></pre>
  
  <p>I want to convert it into csv file like this:</p>
  
  <pre><code>aqi   area    co     co_24h no2 no2_24h o3 o3_24h o3_8h o3_8h_24h pm10
  142   石家庄   1.509  1.412  95      47  3    137    35        90  119
  pm10_24h pm2_5 pm2_5_24h position_name primary_pollutant  quality so2
  195      80    108       化工学校       颗粒物(PM2.5)       轻度污染 33
  so2_24h station_code           time_point
  32        1028A 2013-07-15T23:00:00Z
  </code></pre>
  
  <p>I used as.data.frame() and other functions, but it didn't work.
  How can I do this? Please help me, thanks.</p>