title: pandas - How do I access row in a dataframe by row Index
body: <p>I have a dataframe with 5 rows on which I am doing some validations. If the row does not pass validation, I am adding it to a second dataframe named ValidationFailedDataFrame.</p>
  
  <p>It is OK for the first validation but for the second validation, I want to check if the particular row is already added to the ValidationFailedDataFrame or not and if it is, I want to grab that row and append the error message.</p>
  
  <p>This is how my ValidationFailedDataFrame looks like:</p>
  
  <p><a href="https://i.stack.imgur.com/4zRaQ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/4zRaQ.png" alt="enter image description here"></a></p>
  
  <p>As you can see in the picture, the row that failed the validation was 4th row in the original DataFrame.</p>
  
  <p>How do I query ValidationFailedDataFrame saying give me 4th row of Original DataFrame if you have?</p>