python 用lambda函数替换for循环的方法

import pandas as pd
list = [98,88,37,68,86,33]
df = pd.DataFrame(list, columns=['score']) # convert list to dataframe
df['level'] = '' # add a column
def judgeLevel(df):
 for i in range(len(df)):
  if df.score.ix[i] < 60:
   df.level.ix[i] = 'C'
  elif df.score.ix[i] > 90:
   df.level.ix[i] = 'A'
  else:
   df.level.ix[i] = 'B'
 return df
df = judgeLevel(df)

import pandas as pd 
 
list = [98,88,37,68,86,33] 
 
df = pd.DataFrame(list, columns=['score']) 
 
df['level'] = '' # add a column 
 
def judgeLevel(df): 
 if df['score'] < 60: 
  return 'C' 
 elif df['score'] > 90: 
  return 'A' 
 else: 
  return 'B' 
 
df['level'] = df.apply(lambda r: judgeLevel(r), axis=1)