title: Frequency table using dplyr package
body: <p>I am very new to R.I want to create a new frequency column based on a particular column.</p>
  
  <pre><code>City    age
  ABC     47
  AAB     48
  AAB     41
  AAB     984
  ZZZ     984
  MNO      1
  MNO     34
  VVC     34
  VVC     36
  VVC     41
  VVC     32
  MNO     20
  BB      29
  VVC     4
  VVC    984
  VVC     59
  ABC     30
  ABC    984
  ABC     36
  BB      69
  ABC     32
  ZZZ     3
  ABC     29
  ABC     29
  AAB     1
  AAB     984
  ABC     59 
  </code></pre>
  
  <p>I want data frame looks like -</p>
  
  <pre><code>City    age     Frequency
  ABC     47      0.296296296
  AAB     48      0.185185185
  AAB     41      0.185185185
  AAB     984     0.185185185
  ZZZ     984     0.074074074
  MNO     1       0.111111111
  MNO     34      0.111111111
  VVC     34      0.259259259
  VVC     36      0.259259259
  VVC     41      0.259259259
  VVC     32      0.259259259
  MNO     20      0.111111111
  BB      29      0.074074074
  VVC     4       0.259259259
  VVC     984     0.259259259
  VVC     59      0.259259259
  ABC     30      0.296296296
  ABC     984     0.296296296
  ABC     36      0.296296296
  BB      69      0.074074074
  ABC     32      0.296296296
  ZZZ     3       0.074074074
  ABC     29      0.296296296
  ABC     29      0.296296296
  AAB     1       0.185185185
  AAB     984     0.185185185
  ABC     59      0.296296296
  </code></pre>
  
  <p>In frequency column, I used this formula -</p>
  
  <pre><code>ABC   8             0.296296296 (8/27)
  MNO   3             0.111111111 (3/27)
  BB    2             0.074074074 (2/27)
  VVC   7             0.259259259 (7/27)
  ZZZ   2             0.074074074 (2/27)
  AAB   5             0.185185185 (5/27)
  </code></pre>
  
  <p>You can ignore 'Age' column. How to do it in R?</p>
  
  <p>Thanks in advance.</p>
  
  <p>Regards,
  John</p>