title: Count number of times each unique value appearing in R
body: <p>I have a value arm_index which contains 46095 strings. If you do </p>
  
  <pre><code>&gt; unique(arm_index)
   [1] "NULL"     "CMT1Y"    "TREAS6M"  "LIBOR6M"  "LIBOR1Y"  "COFI11TH"  "CMT5Y"    "TREAS1M" 
   [9] "CMT3Y"    "LIBOR1M"  "CMT6M"    "PRIMEWSJ"
  &gt; length(arm_index)
   [1] 46095
  </code></pre>
  
  <p>I want to find out how many times each unique value appearing here. Like the string "CMT1Y", how many times this string appearing. I am relatively new to R and done some research but couldn't find anything useful. Any suggestion will be greatly appreciated.  </p>