title: R: Calculate standard deviation in cols in a data.frame despite of NA-Values
body: <p>Good Morning,
  I got a lot of data and i have to calculate with it. There are 25 columns (variables) and each column contains thousands of values. But also missing values.
  I calculated the mean with</p>
  
  <pre><code>colMeans(df, na.rm = TRUE)
  </code></pre>
  
  <p>How can i calculate the sd of each column and ignore the NA-values?</p>