Extracting stuff from objects has always been one of the most confusing aspects of R to me. I've fitted a bayesian linear regression model using rjags and have the following mcmc object:

```
summary(m_csim)
Iterations = 1:150000
Thinning interval = 1 
Number of chains = 1 
Sample size per chain = 150000 

1. Empirical mean and standard deviation for each variable,
   plus standard error of the mean:

            Mean        SD  Naive SE Time-series SE
BR2     0.995805 0.0007474 1.930e-06      3.527e-06
BR2adj  0.995680 0.0007697 1.987e-06      3.633e-06
b[1]   -5.890842 0.1654755 4.273e-04      1.289e-02
b[2]    1.941420 0.0390239 1.008e-04      1.991e-03
b[3]    1.056599 0.0555885 1.435e-04      5.599e-03
sig2    0.004678 0.0008333 2.152e-06      3.933e-06

2. Quantiles for each variable:

            2.5%       25%       50%       75%    97.5%
BR2     0.994108  0.995365  0.995888  0.996339  0.99702
BR2adj  0.993932  0.995227  0.995765  0.996229  0.99693
b[1]   -6.210425 -6.000299 -5.894810 -5.784082 -5.55138
b[2]    1.867453  1.914485  1.940372  1.967466  2.02041
b[3]    0.942107  1.020846  1.057720  1.094442  1.16385
sig2    0.003321  0.004082  0.004585  0.005168  0.00657

```

In order to extract the coefficients' means I did `b = colMeans(mod_csim)[3:5]`. I want to calculate credible intervals so I need to extract the 0.025 and 0.975 quantiles too. How do I do that programmatically ?