title: perform acf plot for each type of group in R
body: <p>Say, here the mydata (little part)</p>
  
  <pre><code>transport&lt;- structure(list(date = structure(c(1L, 2L, 3L, 4L, 5L, 6L, 7L, 
  8L, 9L, 10L, 11L, 12L, 1L, 2L, 3L, 4L, 5L, 6L, 7L, 8L, 9L, 10L, 
  11L, 12L), .Label = c("01.01.2001", "01.02.2001", "01.03.2001", 
  "01.04.2001", "01.05.2001", "01.06.2001", "01.07.2001", "01.08.2001", 
  "01.09.2001", "01.10.2001", "01.11.2001", "01.12.2001"), class = "factor"), 
      Market_82 = c(7000L, 7272L, 7668L, 7869L, 8057L, 8428L, 8587L, 
      8823L, 8922L, 9178L, 9306L, 9439L, 3725L, 4883L, 8186L, 7525L, 
      6335L, 4252L, 5642L, 1326L, 8605L, 3501L, 1944L, 7332L), 
      transport = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
      1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L
      ), .Label = c("plane", "train"), class = "factor")), .Names = c("date", 
  "Market_82", "transport"), class = "data.frame", row.names = c(NA, 
  -24L))
  </code></pre>
  
  <p>group variable - Transport.</p>
  
  <p>For each type of transport i must get <code>acf plot</code> of time series.</p>
  
  <p>something like this
  <a href="https://i.stack.imgur.com/04TR1.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/04TR1.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/wlGU5.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/wlGU5.jpg" alt="enter image description here"></a></p>
  
  <p>How perform acf plot for each transport?
  I have a lot of groups. How to do that plots were in folder
  C:/Users/admin/Documents/myplot</p>