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<h2 id="error-returned-when-attempting-to-calculate-mean-of-data.frame-rows">Error returned when attempting to calculate mean of data.frame rows</h2>
<p>As of R version 3.0.0 one cannot use functions such as <code>mean()</code>, <code>max()</code>, <code>min()</code>, etc., on <code>data.frame</code> rows. This can be a problem when going through material in the <a href="02-func-R.html">Creating functions</a> lesson, <strong>Testing and Documenting</strong> section, if one attempts to apply any of these functions to the example dataset rows (e.g., <code>center(dat[4, ], 0)</code>. The examples in the lesson are all written to work only with columns, but an error is returned if one tries using rows. This may also be a problem if one attempts to calculate row means or medians in the <a href="01-starting-with-data.html">Analyzing patient data</a> lesson, <strong>Manipulating Data</strong> section. The <strong>recommended solution</strong> to this issue is to not apply these functions to <code>data.frame</code> rows. However, one <em>could</em> get around this issue by using the functions <code>rowSums</code> or <code>rowMeans</code> in some cases, or explicitly converting the row to a vector of numeric values (e.g., <code>center(as.numeric(dat[4, ]), 0)</code>)</p>
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