title: Adding value from one data.frame to another data.frame by matching a variable
body: <p>Suppose I have two data frames df1 and df2 as follows</p>
  
  <pre><code>Df1
  
  Id Price Profit Month
  10  5     2      1
  10  5     3      2
  10  5     2      3
  11  7     3      1
  11  7     1      2
  12  0     0      1
  12  5     1      2
  
  Df2
  
  Id Name
  9  Kane
  10 Jack
  10 Jack
  11 Will
  12 Matt
  13 Lee
  14 Han
  </code></pre>
  
  <p>Now I want to insert a new column in <code>Df1</code> named <code>Name</code> and get its value from <code>Df2</code> based on matching <code>Id</code></p>
  
  <p>So modified Df1 will be </p>
  
  <pre><code>Id Price Profit Month Name
  10  5     2      1    Jack
  10  5     3      2    Jack
  10  5     2      3    Jack
  11  7     3      1    Will
  11  7     1      2    Will
  12  0     0      1    Matt
  12  5     1      2    Matt
  </code></pre>