This may be a duplicate of the following: [Multiple form submit](https://drupal.stackexchange.com/questions/28585/multiple-form-submit), but I am unable to figure out how the answer applies to my situation.  So here is my go at asking this (I admit) quite similar question:

I have a table with a row of data, each row has a submit button.  It may look something like this:

    $form['f'] = array();
    foreach ($rows as $row) {
      $form['f'][$row['nid']] = array();
      $form['f'][$row['nid']]['nid'] = array(
        '#markup' => $row['nid'],
      );
      $form['f'][$row['nid']]['submit'] = array(
        '#type' => 'submit',
        '#value' => t('sumbit'),
        '#submit' =>  array('f_submit'),
      );
    }

I.e. the form consists of a sequence of rows, extracted from the database,  I want to create a submit callback that picks up the value of the corresponding `nid` field and prints out its value.   I guess I am asking what to put where the comment below is.

    function f_submit($form, &$form_state) {
      // Here I want to print the value of the relevant nid field
    }