title: Grouping numbers for a histogram
body: <p>I have a bunch of numbers I want to use to generate a histogram for a standard score.</p>
  
  <p>Therefore I compute the mean and the standard deviation of the numbers and normalize each x with this formula</p>
  
  <p>x' = (x-mean)/std_dev</p>
  
  <p>The result is a number between -4 and 4. I want to chart that result. I am looking for a way to group the numbers in order to avoid to small bars.</p>
  
  <p>My plan is to have bins in the interval [-4,4] centered at consecutavice quarter units, i.e [-4,-3.75,...,3.75,4]</p>
  
  <p>Example: 0.1 => bin "0.0", 0.3 => bin "0.25", -1.3 => Bin "-1.5"</p>
  
  <p>What is the best way to achieve that?</p>