title: How to set colours in biplot PCA analysis in R
body: <p>Im very new to the R environment and started using it on a practice file.
  i'v created a biplot (biplot is what im required to do) and mange to choose the PC's i wanted. Iv looked for an answer which might be there but i dont understand all the arguments meaning yet and so i might missed the answer.</p>
  
  <pre><code>mat=read.csv('data.txt',sep="\t",row.name=1,check.names=F,header=T)
  mat_as_matrix&lt;-as.matrix(mat)
  tmat=t(mat_as_matrix)
  pca_tmat=prcomp(tmat)
  biplot(pca_tmat, choices=c(3,4), col=c("blue","green"))
  </code></pre>
  
  <p>My input data is like that:</p>
  
  <pre><code>Taxon   S1  S2  S3  S4  S5  S6  S7  S8  S9  S10 S11
  OTU1    45  32  34  55  32  4   12  2   1   4   15
  OTU2    1   2   3   2   1   23  32  21  26  34  23
  OTU3    1   1   2   1   3   1   2   1   2   1   1
  OTU4    12  21  23  45  31  342 342 345 333 322 150
  </code></pre>
  
  <p>I also made a few attemts like the following to remove the arrows. i'm trying to remove the OTU's lables and turn the 'Sn' labels to be points</p>
  
  <pre><code>biplot(pca_tmat$x,pca_tmat$y,type="p", var.axes = F, choices=c(3,4), col=c('blue','green')['S1','S3'])
  </code></pre>
  
  <p>but i get the following error without any changes:
  Error in 1L:p : argument of length 0</p>
  
  <p>What i need to do is to give each sample a different color: Sx, Sy,Sz 1st color Si, Sj 2nd color, Sa,Sb 3rd color, etc...</p>