title: Find single exon models that are part of a multi exon gene
body: <p>I have sets of models which includes single exon models and multi exon models (.psl). I have to find single exon models which are part of multi exon models</p>
  <pre><code>names(a)
  [1] &quot;qseqid&quot;    &quot;a_stitle&quot;  &quot;a_qlen&quot;    &quot;a_slen&quot;    &quot;a_length&quot;  &quot;a_qstart&quot;  &quot;a_qend&quot;    &quot;a_sstart&quot; &quot;a_send&quot;    &quot;a_evalue&quot;  &quot;a_pident&quot;  &quot;a_qcovs&quot;   &quot;a_qcovhsp&quot;
  </code></pre>
  <p>How to write a code to compare sstart and send of models?</p>
  <p>Expected output (data frame):</p>
  <pre><code>Mult_model      Sing_models
  m_qseqid_1      s_qseqid_1, s_qseqid_2 ...
  m_qseqid_2      s_qseqid_3
  m_qseqid_3      s_qseqid_4, s_qseqid_5 ...
  </code></pre>