title: Pandas: using iloc to retrieve data does not match input index
body: <p>I have a dataset which contains contributor's id and contributor_message. I wanted to retrieve all samples with the same message, say, contributor_message == 'I support this proposal because...'. </p>
  
  <p>I use data.loc[data.contributor_message == 'I support this proposal because...'].index -> so basically you can get the index in the DataFrame with the same message, say those indices are 1, 2, 50, 9350, 30678,...</p>
  
  <p>Then I tried data.iloc[[1,2,50]] and this gives me correct answer, i.e. the indices matches with the DataFrame indices.</p>
  
  <p>However, when I use data.iloc[9350] or higher indices, I will <strong>NOT</strong> get the corresponding DataFrame index. Say I got 15047 in the DataFrame this time.</p>
  
  <p>Can anyone advise how to fix this problem?</p>