title: Leave one out cross validation manually
body: <p>I'm trying to create a manual leave one out cross validation. </p>
  
  <p>I have my code here and ironslag contains 53 values. However, my fitted model only contains 52 so I was wondering what I did wrong. </p>
  
  <pre><code>
  for(i in 1:53){
  
    validation&lt;-ironslag[i,]
    training&lt;-ironslag[-i,]
    model1&lt;-lm(magnetic ~ chemical, data = training)
  
    fitted_value &lt;- predict(model1, training)}
  </code></pre>