Exercise 13

This particular Automobile Data Set includes a good mix of categorical values as well as continuous values and serves as a useful example that is relatively easy to understand. Since domain understanding is an important aspect when deciding how to encode various categorical values - this data set makes a good case study.

Read the data into Pandas


In [1]:
import pandas as pd

# Define the headers since the data does not have any
headers = ["symboling", "normalized_losses", "make", "fuel_type", "aspiration",
           "num_doors", "body_style", "drive_wheels", "engine_location",
           "wheel_base", "length", "width", "height", "curb_weight",
           "engine_type", "num_cylinders", "engine_size", "fuel_system",
           "bore", "stroke", "compression_ratio", "horsepower", "peak_rpm",
           "city_mpg", "highway_mpg", "price"]

# Read in the CSV file and convert "?" to NaN
df = pd.read_csv("http://mlr.cs.umass.edu/ml/machine-learning-databases/autos/imports-85.data",
                  header=None, names=headers, na_values="?" )
df.head()


Out[1]:
symboling normalized_losses make fuel_type aspiration num_doors body_style drive_wheels engine_location wheel_base ... engine_size fuel_system bore stroke compression_ratio horsepower peak_rpm city_mpg highway_mpg price
0 3 NaN alfa-romero gas std two convertible rwd front 88.6 ... 130 mpfi 3.47 2.68 9.0 111.0 5000.0 21 27 13495.0
1 3 NaN alfa-romero gas std two convertible rwd front 88.6 ... 130 mpfi 3.47 2.68 9.0 111.0 5000.0 21 27 16500.0
2 1 NaN alfa-romero gas std two hatchback rwd front 94.5 ... 152 mpfi 2.68 3.47 9.0 154.0 5000.0 19 26 16500.0
3 2 164.0 audi gas std four sedan fwd front 99.8 ... 109 mpfi 3.19 3.40 10.0 102.0 5500.0 24 30 13950.0
4 2 164.0 audi gas std four sedan 4wd front 99.4 ... 136 mpfi 3.19 3.40 8.0 115.0 5500.0 18 22 17450.0

5 rows × 26 columns


In [4]:
df.shape


Out[4]:
(205, 26)

In [2]:
df.dtypes


Out[2]:
symboling              int64
normalized_losses    float64
make                  object
fuel_type             object
aspiration            object
num_doors             object
body_style            object
drive_wheels          object
engine_location       object
wheel_base           float64
length               float64
width                float64
height               float64
curb_weight            int64
engine_type           object
num_cylinders         object
engine_size            int64
fuel_system           object
bore                 float64
stroke               float64
compression_ratio    float64
horsepower           float64
peak_rpm             float64
city_mpg               int64
highway_mpg            int64
price                float64
dtype: object

In [3]:
obj_df = df.select_dtypes(include=['object']).copy()
obj_df.head()


Out[3]:
make fuel_type aspiration num_doors body_style drive_wheels engine_location engine_type num_cylinders fuel_system
0 alfa-romero gas std two convertible rwd front dohc four mpfi
1 alfa-romero gas std two convertible rwd front dohc four mpfi
2 alfa-romero gas std two hatchback rwd front ohcv six mpfi
3 audi gas std four sedan fwd front ohc four mpfi
4 audi gas std four sedan 4wd front ohc five mpfi

In [ ]:

Exercise 13.1

Does the database contain missing values? If so, replace them using one of the methods explained in class


In [ ]:

Exercise 13.2

Split the data into training and testing sets

Train a Random Forest Regressor to predict the price of a car using the numeric features


In [ ]:

Exercise 13.3

Create dummy variables for the categorical features

Train a Random Forest Regressor and compare


In [ ]:

Exercise 13.4

Apply two other methods of categorical encoding

compare the results


In [ ]: