title: locate missingness in fitted model in R
body: <p>Consider fitting a <code>coxph</code> model with, say, 100 data points. Only 95 are included in the analysis, while 5 are excluded due to being <code>NA</code> (i.e. missingness). I extract the residuals on the fitted data so I have a residual vector with 95 observations. I would like to include the residuals back into the original data frame, but I can't do this since the lengths are different. </p>
  
  <p>How do I identify which observations from the original data frame were not included in the model, so I can exclude/delete them to make the two lengths the same? </p>
  
  <p>(The original data is much larger so it's hard to locate where data are missing...)</p>