title: how to extract upper/lower bounds on coefficients from quantile regression rq()
body: <p>I'd like to extract coefficients and upper and lower bounds from a quantile regression using the <code>quantreg</code> package. Here's an example from the help file.</p>
  
  <pre><code>data(engel)
  attach(engel)
  taus &lt;- c(.05,.1,.25,.75,.9,.95)
  f &lt;- rq((foodexp)~(income),tau=taus)
  sf &lt;- summary(f)
  sf[1]
  #[[1]]
  
  #Call: rq(formula = (foodexp) ~ (income), tau = taus)
  
  #tau: [1] 0.05
  
  #Coefficients:
  #            coefficients lower bd  upper bd 
  #(Intercept) 124.88004     98.30212 130.51695
  #income        0.34336      0.34333   0.38975
  </code></pre>
  
  <p>I know I can use <code>coefficients()</code> to get the coefficients.</p>
  
  <pre><code>cf &lt;- t(data.frame(coefficients(f)))    # transpose for better arrangement
  cf
  #              (Intercept)    income
  #tau..0.05   124.88004 0.3433611
  #tau..0.10   110.14157 0.4017658
  #tau..0.25    95.48354 0.4741032
  #tau..0.75    62.39659 0.6440141
  #tau..0.90    67.35087 0.6862995
  #tau..0.95    64.10396 0.7090685
  </code></pre>
  
  <p>But I can't figure out how to get the upper/lower bounds that appear in <code>summary()</code>. I looked at <code>str(sf)</code>, but I did not see how to extract. </p>
  
  <p>Ultimately, I'd like to put taus, coefficients, and upper/lower bounds in a dataframe for further processing.</p>