title: How to do random sampling based on customer ID
body: <p>I have a data set as below</p>
  
  <pre>
  Cust_ID SubDepartment       Date        Bill_Value
  1513    Detergent Bars      20180204    30
  1513    French Fries        20180803    160
  1513    Fruit Based Juices  20180204    30
  1513    Containers          20180803    79
  1513    Candies & Lollypops 20180803    165
  1513    Cheese              20180204    203.04
  1513    Cleaners & Wipers   20180803    159
  1513    Chocolates          20180803    448
  1513    Frozen Veg Snacks   20180803    570
  1860    Salted Biscuits     20180110    40
  1860    Oats                20180705    60
  1860    Pastries            20180815    198
  1860    Cheese              20180110    85
  1860    Veg Powdered Soups  20180814    20
  1860    Paneer              20180123    99
  1860    North Indian Mixes  20180502    59
  1860    Flavoured Milk      20180502    40
  </pre>
  
  <p><a href="https://i.stack.imgur.com/Uo9BQ.jpg" rel="nofollow noreferrer">sample data set</a></p>
  
  <p>I have want to do random sampling of the data based on customer id such that it picks all the transaction of the selected customers</p>