title: How to get the mean from mcmc.list object?
body: <p><code>output = RBugsfit(..., coda=T, ...)</code> output a mcmc.list object, which contains samples of the posterior distributions of four parameters, and their sample posterior means. Using <code>summary()</code> I can see the sample posterior means, but I wonder how to retrieve the sample posterior means from <code>output</code> into a variable in my program? Thanks!</p>
  
  <pre><code>&gt; summary(output)
  
  Iterations = 201:3396
  Thinning interval = 5 
  Number of chains = 2 
  Sample size per chain = 640 
  
  1. Empirical mean and standard deviation for each variable,
     plus standard error of the mean:
  
             Mean        SD  Naive SE Time-series SE
  beta  1.052e+00 3.189e-02 8.914e-04      9.185e-04
  df    3.849e+00 2.916e-01 8.150e-03      1.516e-02
  sigma 1.056e-02 2.504e-04 6.998e-06      1.000e-05
  tau   8.990e+03 4.273e+02 1.194e+01      1.710e+01
  
  2. Quantiles for each variable:
  
             2.5%       25%       50%       75%     97.5%
  beta  9.891e-01 1.032e+00 1.052e+00 1.073e+00 1.113e+00
  df    3.304e+00 3.650e+00 3.836e+00 4.042e+00 4.450e+00
  sigma 1.004e-02 1.039e-02 1.055e-02 1.072e-02 1.105e-02
  tau   8.197e+03 8.700e+03 8.977e+03 9.263e+03 9.917e+03
  
  &gt; str(output)
  List of 2
   $ : mcmc [1:640, 1:4] 1.1 1.03 1.05 1.12 1.07 ...
    ..- attr(*, "dimnames")=List of 2
    .. ..$ : NULL
    .. ..$ : chr [1:4] "beta" "df" "sigma" "tau"
    ..- attr(*, "mcpar")= num [1:3] 201 3396 5
   $ : mcmc [1:640, 1:4] 1.03 1.04 1.06 1.06 1.07 ...
    ..- attr(*, "dimnames")=List of 2
    .. ..$ : NULL
    .. ..$ : chr [1:4] "beta" "df" "sigma" "tau"
    ..- attr(*, "mcpar")= num [1:3] 201 3396 5
   - attr(*, "class")= chr "mcmc.list"
  </code></pre>