title: Filtering CSV files
body: <p>I have a csv file and another text file (say file1.csv and file2.txt). The text file has one column. Now, I want to filter the csv file based on the data in the text file. For example,</p>
  
  <pre>
  file1.csv
  -----------
  1,a,b,c
  2,d,e,f
  3,g,d,g
  
  file2.txt
  -----------
  1
  3
  </pre>
  
  <p>I want the result to be-</p>
  
  <pre>
  1,a,b,c
  3,g,d,g
  </pre>