将列的数据转换为枚举字典键值

Question

是否有更好的方法（在最小代码的意义上）可以执行以下操作：将列转换为枚举数值，所以它应该有点这样：

1. 在列中获取一组项
2. 制作带有键值的枚举字典
3. 用值还原键
4. 使用键值结果代替新列中的数据。

这就是我今天要做的事情，想知道是否有人可以展示一个经典的方法来做到这一点，这样我就可以避免编写函数get_color_val：

import pandas as pd  
cars = pd.DataFrame({"car_name": ["BMW","BMW","ACCURA","ACCURA","ACCURA","BMW","BMW","BMW"],"color":["RED","RED","RED","RED","GREEN","BLACK","BLUE","BLUE"]})

color_dict = dict(enumerate(set(cars["color"])))
color_dict = dict((y,x) for x,y in color_dict.iteritems())

def get_color_val(row):
    my_key = row["color"]
    my_value = color_dict.get(my_key)
    return my_value

cars["color_val"] = cars.apply(get_color_val, axis=1)
cars = cars.drop("color",1)
print cars

结果

Before------------
car_name  color
0      BMW    RED
1      BMW    RED
2   ACCURA    RED
3   ACCURA    RED
4   ACCURA  GREEN
5      BMW  BLACK
6      BMW   BLUE
7      BMW   BLUE


After------------
car_name  color_val
0      BMW          3
1      BMW          3
2   ACCURA          3
3   ACCURA          3
4   ACCURA          2
5      BMW          1
6      BMW          0
7      BMW          0

Answer 1

在这种情况下我会使用pd.factorize()：

In [8]: cars['color_val'] = pd.factorize(cars.color)[0]

In [9]: cars
Out[9]:
  car_name  color  color_val
0      BMW    RED          0
1      BMW    RED          0
2   ACCURA    RED          0
3   ACCURA    RED          0
4   ACCURA  GREEN          1
5      BMW  BLACK          2
6      BMW   BLUE          3
7      BMW   BLUE          3