title: Create subset and overall value line chart
body: <p>This may sounds very simple but I am finding hard to get that. I have a data with value in one column and category in another column. i.e.,</p>
  
  <pre><code>Value Category Month
  100     A       Jan
  300     A       Feb
  200     A       Mar
  459     B       Jan
  334     B       Feb
  765     B       Mar
  </code></pre>
  
  <p>I am trying to use a line chart in tableau with Month on X axis and Value on Y-axis.Basically I am trying to add two lines, one for overall value for that particular month and another line for Category A alone for that particular month. Say for example the overall value for Jan as 559 and another line in same graph for category A for Jan as 100.</p>
  
  <p>Though it sounds so basic, I find hard to achieve this. Should I create a calculated field for this or is there any simple method that works for this.</p>