# Applying Correlation as a Criterion in Hierarchical Decision Trees

Decision trees are a simple yet powerful method of machine learning. A binary tree is constructed in which the leaf nodes represent predictions. The internal nodes are decision points. Thus, paths from the root to the leafs represent sequences of decisions that result in an ultimate prediction.

Decision trees can also be used in hierarchical models. For instance, the leafs can instead represent subordinate models. Thus, a path from the root to a leaf node is a sequence of decisions that result in a prediction made by a subordinate model. The subordinate model is only responsible for predicting samples that fall within the leaf.

This post presents an approach for a hierarchical decision tree model with subordinate linear regression models.

# A Method for Addressing Nonhomogeneous Data using an Implicit Hierarchical Linear Model

Datasets containing nonhomogenous groups of samples present a challenge to linear models. In particular, such datasets violate the assumption that there is a linear relationship between the independent and dependent variables. If the data is grouped into distinct clusters, linear models may predict responses that fall in between the clusters. These predictions can be quite far from the targets depending on how the data is structured. In this post, a method is presented for automatically handling nonhomogenous datasets using linear models.

# Decorrelating Features using the Gram-Schmidt Process

A problem that frequently arises when applying linear models is that of multicollinearity. The term multicollinearity describes the phenomenon where one or more features in the data matrix can be accurately predicted using a linear model involving others of the features. The consequences of multicollinearity include numerical instability due to ill-conditioning, and difficulty in interpreting the regression coefficients. An approach to decorrelate features is presented using the Gram-Schmidt process.

# TVLib: A C++ Text Vectorization Library with Python Bindings

I am a big fan of the CountVectorizer class in scikit-learn [1]. With a robust and easy interface that produces (sparse!) matrices, what’s not to love? Well, it’s… pretty… slow…

The performance is okay for 10s of MB of text, but GBs take minutes or more. It terms out that CountVectorizer is implemented in pure Python. The functions are single threaded too. It seems like low-hanging fruit. Just whip up some parallel C++, right? Well, not quite, but I’m getting ahead of myself.

# On the Analysis and Prediction of Recessions in the USA

This chapter explores recessions in the United States of America. Datasets are collected from a variety of locations including the Federal Reserve Economic Data (FRED) and from the website of Yale professor and Nobel laureate Dr. Robert J. Shiller. A classifier model is constructed which predicts recessions and this model is analyzed for useful insights.

# Real S&P Composite Moving Average

Recently, I have been experimenting with windowing functions for time series data. While trying out my code, I came up with a nice and (somewhat) thought-provoking plot.

# A Brief Analysis of Survey Data from a Speed Dating Event

In this post, survey data collected from several speed dating events is analyzed. The events were conducted between 2002 and 2004 by two professors from Columbia University: Ray Fisman and Sheena Iyengar. In addition to questions about personal interests, the survey includes academic and occupational questions as well.