title: Keep all variables after every iteration
body: <p>Using the following snippet it is possible to iterate two api call in json format</p>
  <p>At the end of the loop there is a command with transforms json to data frame</p>
  <p>How is it possible to keep in every iteration all these variables and fill NA if a value in the specific variable does not exist in a specific iteration?</p>
  <pre><code>library(jsonlite)
  library(httpuv)
  library(httr)
  
  myapp &lt;- oauth_app(appname = &quot;insert_your_credentials&quot;,
                     key = &quot;insert_your_credentials&quot;,
                     secret = &quot;insert_your_credentials&quot;)
  
  github_token &lt;- oauth2.0_token(oauth_endpoints(&quot;github&quot;), myapp)
  
  
  gtoken &lt;- config(token = github_token)
  
  df &lt;- data.frame(link = c(&quot;https://api.github.com/search/commits?q=%22image%22+AND+%22covid%22?page=1&amp;per_page=100&quot;, &quot;https://api.github.com/search/commits?q=%22image%22+AND+%22covid%22?page=2&amp;per_page=100&quot;))
  
  
  for (i in 1:nrow(df)) {
  
      req &lt;- GET(df$link[i])
      
      # Extract content from a request
      json1 = content(req)
        
        # Convert to a data.frame
    
      char &lt;- rawToChar(req$content)
      dfcollection &lt;- jsonlite::fromJSON(char)
      
  }
  </code></pre>