title: how to find index of match between two set of data frame
body: <p>Two data frame with one being my reference </p>
  
  <pre><code>df1&lt;- structure(list(V1 = structure(c(2L, 14L, 8L, 12L, 1L, 3L, 4L, 
  5L, 6L, 9L, 10L, 16L, 7L, 15L, 11L, 13L), .Label = c("A", "AbC", 
  "B", "C", "D", "F", "FFFS", "G6_7", "GI666", "GTJJJ", "HINDO", 
  "MirTn", "Mumbai", "NdFi1", "TRS100", "TTTNKK"), class = "factor"), 
      V2 = c(10L, 22L, 33L, 35L, 89L, 6L, 973L, 686L, 82L, 22L, 
      1L, 82L, 1L, 9304L, 43L, 736L)), .Names = c("V1", "V2"), class = "data.frame", row.names = c(NA, 
  -16L))
  
  
  df2&lt;- structure(list(V1 = structure(c(1L, 4L, 5L, 3L, 2L, 6L), .Label = c("AbC", 
  "Bangalore", "Dehli", "F", "GI666", "Mumbai"), class = "factor")), .Names = "V1", class = "data.frame", row.names = c(NA, 
  -6L))
  </code></pre>
  
  <p>I want to find the index of those that match and a dash for those that are not match between df1$V1 and df2$V1</p>
  
  <p>I tried to do it with no success, it is because the R is repeating the index over the column </p>
  
  <pre><code>df1$myindex &lt;- as.character(which(df1$V1 %in% df2$V1))
  </code></pre>
  
  <p>what I am looking for is shown below </p>
  
  <pre><code>#         V1 myindex 
  #1       AbC    1
  #2         F    9
  #3     GI666    10
  #4     Dehli    -
  #5 Bangalore    -
  #6    Mumbai    16
  </code></pre>