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A decision tree model based on Melbourne Housing Dataset.
# coding: utf-8
# In[1]:
#Pandas is the primary tool that modern data scientists use for exploring and manipulating data. Let's import it.
import pandas as pd
# In[6]:
#let's load the housing data for melbourne
data_file_path = "/Users/harshvardhan/learning_scikit/data/melb_data.csv" #replace the path with your file path
#panda's read_csv method reads the csv file and loads into a data structure called data_frame
#imagine data_frame as sql table
melbourne_data_frame = pd.read_csv(data_file_path)
#let's show first two rows of the csv/data_frame to get a feel of the data
melbourne_data_frame[:2]
# In[3]:
#Describe method gives us 8 attributes of each column of csv:
#They are 1. Count (Total valid values) 2. Mean (Average) 3. std (Standard Deviation) 4. min (Minimum in that column)
#5. 25% (25th percentile) 6. 50% (50th Percentile) 7. 75% (75th Percentile) 8. Max(Maximum in that column)
melbourne_data_frame.describe()
# In[8]:
#Selecting one column of data frame using panda
price_column = melbourne_data_frame.Price
#head method prints first few data of the column
price_column.head()
# In[10]:
#Selecting more than one coulmn; store the name of coulmn in an array
rooms_price_column_name = ["Rooms","Price"]
rooms_price_column = melbourne_data_frame[rooms_price_column_name]
#Let's verify. Shall we? Again, the head command.
rooms_price_column.head()
# In[11]:
#Let's pick our problem statement. It's kind of simple. We need to build a model to predict price of a house.
#Think of it this way. An old couple Mr. and Mrs. Waugh who owns two houses in Melbourne wants to sell one of
#them. They have all the data of their house ready with them but unfortunately, they don't know the price.
#So, our target is to find price and consequently we will name Price as target column. Follwing the general tradition,
# where function is written as y = f(x), we will call price column as y.
y = price_column
# In[39]:
#Now, let's talk about f(x) here. To start with, let's assume that out of several data given about the house; we think
# that the price of house in melbourne depends on number of rooms, number of bathroom, landsize, building area, and
#year in which it is built. we will call them predictors of price. Obviously, price depends on other factors. But
#what the heck, let's get started.
melbourne_price_predictors_coulmn = ['Rooms', 'Bathroom', 'Landsize', 'BuildingArea','YearBuilt']
#Going with tradition, thse are variables x of function f(x)
X_raw = melbourne_data_frame[melbourne_price_predictors_coulmn]
# In[40]:
#What is the our input has bad values or missing values? Imputer replaces those missing values with some other value.
from sklearn.preprocessing import Imputer
my_imputer = Imputer()
X = my_imputer.fit_transform(X_raw)
# In[42]:
#here, we split the given data in 2 parts. one for making model and other for validating it.
#train_X is training and val_X is for validating the data.
from sklearn.model_selection import train_test_split
train_X, val_X, train_y, val_y = train_test_split(X, y,random_state = 0)
# In[43]:
#we have x and y. Where is f(x)?
#so f(x) here is decision tree model. Read the blog text to find out about decision tree. scikit provides us
#several models (f(x)) to predict a quantity. They are of several kinds..decision Tree, Logistic Regression,
#Linear Regression. In terms of usage, it does the same work what we used to do in cartesian plane by extending
#the straight line (Remember regression?) All the scikit regression models implement two methods fit() and predict()
#Let's start with importing decision tree regression model
from sklearn.tree import DecisionTreeRegressor
# In[44]:
#We will now tell regressor to give us f(x). we will give x to our regressor, f to give us f(x)
#I hope i am making sense here.
#let's define function f here.
decision_tree_regressor = DecisionTreeRegressor()
#Tell the regressor to act on predictors, x and give us a f(x). This is done by a fit method
decison_tree_model = decision_tree_regressor.fit(train_X, train_y)
# In[51]:
#Ready to test? Let's print the second row of our data frame
val_y
# In[57]:
#the price is 340000.0 for first validation entry,now let's give the same data to our model
predicted_price = decision_tree_regressor.predict(val_X)
print(predicted_price)
# In[59]:
#the model predicted price for the first entry as 46000 which is 12000 off the real price.
#To calculate how good is our model, we are going to find mean absolute error. What is mean absolute error?
# error is real_value - predicted value. mean absolute error is the mean of errors.
#let's find the mean average error for our predicted prices and go home, sleep.
from sklearn.metrics import mean_absolute_error
print(mean_absolute_error(val_y, predicted_price))
# In[ ]:
#395864.829956 is mean error value. That's a very bad mean error value. We are predicting prices too much away from the real one. Let's try to make it better
#next time.
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