title: Why do some datasets need us to do `data(somedataset)` before we can use them?
body: <p>Why do we have to use <code>data(spam)</code> before we can run <code>lda</code> on it ? <code>spam</code> is a dataset in the <code>ElemsStatLearn</code> package. </p>
  
  <pre><code>library(ElemStatLearn)
  library(MASS) # for lda
  spam[5] # is ok
  spam.lda = lda(spam ~ . , data = spam) # not ok
  data(spam)
  spam.lda = lda(spam ~ . , data = spam) # ok 
  </code></pre>
  
  <p>We can access <code>spam[5]</code> even before we run <code>data(spam)</code>.</p>