title: How to apply custom function to pandas data frame for each row
body: <p>I want to apply a custom function and create a derived column called population2050 that is based on two columns already present in my data frame.</p>
  
  <pre><code>import pandas as pd
  import sqlite3
  conn = sqlite3.connect('factbook.db')
  query = "select * from facts where area_land =0;"
  facts = pd.read_sql_query(query,conn)
  print(list(facts.columns.values))
  
  def final_pop(initial_pop,growth_rate):
      final = initial_pop*math.e**(growth_rate*35)
      return(final)
  
  facts['pop2050'] = facts['population','population_growth'].apply(final_pop,axis=1)
  </code></pre>
  
  <p>When I run the above code, I get an error. Am I not using the 'apply' function correctly?</p>