title: How to identify if an observation is repeated every day in Stata
body: <p>I have a database where I have a date variable, an id variable and a city variable. Sometimes the id variable is repeated in the same date and city.
  Data looks something like this:</p>
  
  <blockquote>
    <p>Date        ID     City</p>
    
    <blockquote>
      <p>2/1/2015    1        1</p>
      
      <p>2/1/2015    1        1</p>
      
      <p>2/1/2015    1        2</p>
      
      <p>2/2/2015    1        1</p>
      
      <p>2/1/2015    2        1</p>
      
      <p>2/2/2015    2        1</p>
    </blockquote>
  </blockquote>
  
  <p>I would like to know how much days each ID is present, identify the id's that are present every day, and later on, those that are present every day in every city.
  In the example above both ID 1&amp;2 are present each day, but only ID 1 is present in each city each day.
  Thanks!</p>