title: Automate filter in R
body: <p>studio and I have a data frame with columns a and b.</p>
  
  <pre><code> a        b
   EUR      1
   SGD      2
   AUD      3
   CAD      4
   JPY      5
   HKD      6
  </code></pre>
  
  <p>Right now the data only has 6 rows in total, but in the future, it can look like this. </p>
  
  <pre><code>a        b
   EUR      1
   SGD      2
   AUD      3
   CAD      4
   JPY      5
   HKD      6
   NZD      7
  </code></pre>
  
  <p>Because the data is imported with a new file every day, so I want to automate and only choose column a with <code>"EUR", "USD","NZD"</code>. One of my problem is for the upcoming data frame I don't know if there gonna be NZD or EUR or USD, so I want R to scan it and if there is corresponding value. R will choose it
  Does anyone know how to do it?</p>