title: Add labels to plot for specific values in R
body: <p>I create a plot with the following dataset and I would like to add a label only for points flagged with a T in the "DisplayName" column.</p>
  
  <pre><code>Probe   Name    DisplayName X   Y
  bob1    A   0   53.989643   7935.185
  bob2    B   T   55.11423    7930.626
  bob3    C   0   49.537724   6901.7715
  bob4    D   0   57.280113   6687.0156
  bob5    E   T   7.5517325   840.3756
  bob6    F   0   62.68943    6666.6665
  bob7    G   T   32.553364   3036.508
  bob8    H   0   34.120102   2553.5354
  bob9    I   0   127.54777   7818.89
  </code></pre>
  
  <p>My idea would be to use text() and which() to add the value of "Name" but I am stuck with something like this:</p>
  
  <pre><code>plot(data$X, data$Y)
  text(data$X, data$Y, d$Name[which(d$DisplayName =="T",  arr.ind=TRUE)])
  </code></pre>
  
  <p>Any help will be appreciated,</p>
  
  <p>Cheers ;)</p>