title: Having problem with some packages unloaded
body: <p>I searched through Stackoverflow, but could not find a straightforward answer for my question. So, I want to do ordered logit modeling via using rms package. So, I installed this package, and after calling it through Library, I get the following:  </p>
  
  <pre><code>&gt; library("rms")
  Loading required package: Hmisc
  Loading required package: lattice
  Loading required package: survival
  Loading required package: Formula
  Loading required package: ggplot2
  
  Attaching package: ‘Hmisc’
  
  The following objects are masked from ‘package:base’:
  
      format.pval, units
  
  Loading required package: SparseM
  
  Attaching package: ‘SparseM’
  
  The following object is masked from ‘package:base’:
  
      backsolve
  </code></pre>
  
  <p>So far, it is not a problem. Therefore, I installed all the mentioned packages. Then, again after running Library(rms), I faced the following:</p>
  
  <pre><code>Error: package or namespace load failed for ‘rms’ in loadNamespace(i, c(lib.loc, .libPaths()), versionCheck = vI[[i]]):
   there is no package called ‘zoo’
  </code></pre>
  
  <p>I am confused. I uninstalled RStudio, and re-installed it, but, no change. Also, I have the same issue with other packages. For example, I tried to call package of MASS, same issue.</p>
  
  <pre><code>    &gt; library("MASS", lib.loc="C:/Program Files/R/R-3.5.1/library") 
  Error in value[[3L]](cond) :    
    Package ‘MASS’ version 7.3.51.1 cannot be unloaded:  
  Error in unloadNamespace(package) : namespace ‘MASS’ is imported by ‘rockchalk’, ‘lme4’ so cannot be unloaded
  </code></pre>