title: Filtering a data frame
body: <p>I have read in a csv file in matrix form (having m rows and n columns). I want to filter the matrix by conducting a filter in verbal form: </p>
  
  <p>Select all values from column x where the values of an another column in this row is equal to "blabla".</p>
  
  <p>It is like a select statement in database where I say I am interested in a subset of the matrix where these constraints need to be satisfied. </p>
  
  <p>How can I do it in r? I have the data as dataframe and can access it by the headers. <code>data["column_values" = "15"]</code> does not give me back the rows where the column named column_values have values 15 only. </p>
  
  <p>Thanks </p>