import the librairies

import pandas as pd
import numpy as np
from sklearn import tree
train = pd.read_csv("train.csv")
train.describe()
train.shape
(891,12)

How many people in your training set survived the disaster with the Titanic? To see this, you can use the value_counts() method in combination with standard bracket notation to select a single column of a DataFrame:

Passengers that survived vs passengers that passed away

survived_num = train["Survived"].value_counts()
print(survived_num)

0    549
1    342
Name: Survived, dtype: int64

As proportions

percentage = train["Survived"].value_counts(normalize=True)
print(percentage)

0    0.616162
1    0.383838
Name: Survived, dtype: float64

Males that survived vs males that passed away

male_survived = train["Survived"][train["Sex"] == 'male'].value_counts()
print(male_survived)

0    468
1    109
Name: Survived, dtype: int64

Females that survived vs Females that passed away

female_survived = train["Survived"][train["Sex"] == 'female'].value_counts()
print(female_survived)

1    233
0     81
Name: Survived, dtype: int64

Normalized male survival

nor_male = train["Survived"][train["Sex"] == 'male'].value_counts(normalize = True)
print(nor_male)

0    0.811092
1    0.188908

Name: Survived, dtype: float64

Normalized female survival

nor_female = train["Survived"][train["Sex"] == 'female'].value_counts(normalize = True)
print(nor_female)

1    0.742038
0    0.257962
Name: Survived, dtype: float64

Does Age play a role ?

Another variable that could influence survival is age; since it's probable that children were saved first. You can test this by creating a new column with a categorical variable Child. Child will take the value 1 in cases where age is less than 18, and a value of 0 in cases where age is greater than or equal to 18.

To add this new variable you need to do two things (i) create a new column, and (ii) provide the values for each observation (i.e., row) based on the age of the passenger.

Adding a new column with Pandas in Python is easy and can be done via the following syntax:

train["Child"] = float('NaN')

Assign 1 to passengers under 18, 0 to those 18 or older. Print the new column.

train["Child"][train["Age"] < 18] = 1 
train["Child"][train["Age"] >= 18] = 0

Print normalized Survival Rates for passengers under 18

print (train["Survived"][train["Child"] == 1].value_counts( normalize =  True))
1    0.539823
0    0.460177
Name: Survived, dtype: float64

Print normalized Survival Rates for passengers 18 or older

print(train["Survived"][train["Child"] == 0].value_counts( normalize =   True))
0    0.618968
1    0.381032
Name: Survived, dtype: float64

Convert the male and female groups to integer form

train["Sex"][train["Sex"] == "male"] = 0
train["Sex"][train["Sex"] == "female"] = 1

Impute the Embarked variable

train["Embarked"] = train["Embarked"].fillna("S")

Convert the Embarked classes to integer form

train["Embarked"][train["Embarked"] == "S"] = 0
train["Embarked"][train["Embarked"] == "C"] = 1
train["Embarked"][train["Embarked"] == "Q"] = 2

Print the Sex and Embarked columns

print(train["Sex"])
print(train["Embarked"])

Creating your first decision tree

Print the train data to see the available features

print(train)

Create the target and features numpy arrays: target, features_one

target = train["Survived"].values
features_one = train[["Pclass", "Sex", "Age", "Fare"]].values

Fit your first decision tree: my_tree_one

my_tree_one = tree.DecisionTreeClassifier()
my_tree_one = my_tree_one.fit(features_one,target)

Look at the importance and score of the included features

print(my_tree_one.feature_importances_)
print(my_tree_one.score(features_one,target))

05-05-2016