Lesson 4: Decision Trees

from sklearn.tree import DecisionTreeClassifier
clf = DecisionTreeClassifier(min_samples_split=40)
clf.fit(features_train, labels_train)

UD120 – Intro to Machine Learning

One part of my bucket list for 2018 was finishing the Udacity Course UD120: Intro to Machine Learning.

the host of this course are Sebastian Thrun, ex-google-X and founder of Udacity and Katie Malone, creator of the Linear digressions podcast.

The course consists of 17 lessons. Every lesson has a couple of hours of video and lots and lots of quizzes in it.

  • [x] Lesson 1: Only introduction 🙂
  • [x] Lesson 2: Naive Bayes
  • [x] Lesson 3: Support Vector Machines
  • [x] Lesson 4: Decision Trees
  • [x] Lesson 5: Choose your own algorithm
  • [ ] Lesson 6: Datasets and questions
  • [ ] Lesson 7: Regression
  • Lesson 8: Outliers
  • Lesson 9: Clustering
  • Lesson 10: Feature Scaling
  • Lesson 11: Text Learning
  • Lesson 12: Feature Selection
  • Lesson 13: PCA
  • Lesson 14: Validation
  • Lesson 15: Evaluation Metrics
  • Lesson 16: Tying it all together
  • Lesson 17: Final project

Python pip and virtualenv

After working for a couple of years with Python and external dependencies I’ve ran again and again into the same kind of problems.

Bad habits

Say you have a global python installation under e.g. C:\Python27 on Windows. When you start working on your first python project you want to use external packages and you encounter pip as dependency management tool. (pip is part of the python installation since 2.7.9 / 3.4) So far so good.

But you keep installing all the packages into your global python installation. Continue reading “Python pip and virtualenv”

JavaScript: dot vs bracket notation

During linting my code jshint gave me the “hint” that I should prefer dot notation over bracket notation.

"testcase": data.finding["testcase"], [‘testcase’] is better written in dot notation.

What is that?

  • Accessing members with “.” is called “dot notation”.
  • Accessing them with [] is called “bracket notation”.

 

The Normal Distribution

Diving deeper into data science I started to brush up my knowledge about math especially statistics.

The Mother of all Distributions

The normal distribution was formulated by Carl Friedrich Gauß in 18XX and can be implemented in Python like the following :

def normal_distribution(x, mu=0, sigma=1):
    sqrt_two_pi = math.sqrt(2*math.pi)
    return math.exp(-(x-mu)**2 / 2 / sigma**2) / sqrt_two_pi * sigma

Data Science: Cross-Validation

For validating your model You need to split your data into a training and a test data set.

More training data means a better model, more test data means better validation.

But because the amount of data to train/test the model is limited you have to decide in which ratio of training vs test data you want to split your data.

import numpy as np
from sklearn.model_selection import train_test_split
from sklearn import datasets
from sklearn import svm

iris = datasets.load_iris()
iris.data.shape, iris.target.shape

Sample a training set while holding out 40% of the data for testing:

X_train, X_test, y_train, y_test = train_test_split( iris.data, iris.target, test_size=0.4, random_state=0)
from sklearn.model_selection import cross_val_score
clf = svm.SVC(kernel='linear', C=1)
scores = cross_val_score(clf, iris.data, iris.target, cv=5)

Five Minutes with Ingo: Cross Validation