title: Error in filter_impl(.data, quo) : Result must have length 259, not 399
body: <p>I'm struggling with this error about few hours. I'm not sure how to explain my problem well.</p>
  
  <p>the situation is I was preprocessing some 18 cities' overall excel data by year</p>
  
  <p>for example variable1(numeric) variable2(numeric) </p>
  
  <pre><code>year reg     ....
  2001 11      ...
  2002 21      ...
  2I03 22
  2004 32
  </code></pre>
  
  <p>I want to divide by cities, make new variable which represents each variable's average. after that, make new excel sheet city by city.</p>
  
  <p>so... i typed </p>
  
  <pre><code> for(i in 2:3){
     for(k in 1:9){
        raw_ik &lt;- raw_data %&gt;% 
            filter(reg==ik)
  
            raw_ik_mean &lt;- raw_data%&gt;% 
            filter(reg==ik) %&gt;% 
            summarise(mean_grGo = mean(grGo))
  
            ik&lt;- bind_rows(raw_ik,raw_ik_mean)
      }
   }
  </code></pre>
  
  <p>but, Error in filter_impl(.data, quo) : Result must have length 259, not 399</p>
  
  <p>Thanks in advance.</p>