title: How to divide a table into different levels based on values in R?
body: <p>Suppose that i have following data </p>
  
  <pre><code>ID  Category    Price   Month
  1   X            2       1
  1   X            2       2
  1   X            2       3
  1   X            2       4
  2   X            3       1
  2   X            3       2
  2   X            3       3
  2   X            3       4
  3   X            1       1
  3   X            1       2
  3   X            1       3
  3   X            1       4
  4   X            10      1
  4   X            10      2
  4   X            10      3
  4   X            10      4
  5   Y            5       1
  5   Y            5       2
  5   Y            5       3
  5   Y            5       4
  6   Y            2       1
  6   Y            2       2
  6   Y            2       3
  6   Y            2       4
  7   Y            1       1
  7   Y            1       2
  7   Y            1       3
  7   Y            1       4
  8   Y            10      1
  8   Y            10      2
  8   Y            10      3
  8   Y            10      4
  </code></pre>
  
  <p>There are different prices for products in a particular category, some are low priced and some high priced. I want to have a new variable "<code>Price Level</code>" which shows whether the product is low priced product, medium priced product or high priced product. </p>
  
  <p>Levels are defined as follows. 
  It takes the prices of all the products in a particular category and divide into 4 percentiles.  </p>
  
  <ul>
  <li>1st Percentile  = Low </li>
  <li>2nd and 3rd percentile = Medium</li>
  <li>4th percentile = High</li>
  </ul>
  
  <p>So the table will look like this </p>
  
  <pre><code>ID  Category    Price   Month   Price Level
  1   X            4       1        Medium
  1   X            4       2        Medium
  1   X            4       3        Medium
  1   X            4       4        Medium
  2   X            3       1        Medium
  2   X            3       2        Medium
  2   X            3       3        Medium
  2   X            3       4        Medium
  3   X            1       1        Low
  3   X            1       2        Low
  3   X            1       3        Low
  3   X            1       4        Low
  4   X            10      1        High
  4   X            10      2        High
  4   X            10      3        High
  4   X            10      4        High
  5   Y            5       1        Medium
  5   Y            5       2        Medium
  5   Y            5       3        Medium
  5   Y            5       4        Medium
  6   Y            2       1        Low
  6   Y            2       2        Low
  6   Y            2       3        Low
  6   Y            2       4        Low
  7   Y            1       1        Low
  7   Y            1       2        Low
  7   Y            1       3        Low
  7   Y            1       4        Low
  8   Y            10      1        Low
  8   Y            10      2        Low
  8   Y            10      3        Low
  8   Y            10      4        Low
  </code></pre>