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#### Moving to aaronschlegel.me

Hello, Everyone! First of all, I want to thank everyone who has visited my site over the years. I hope my posts have been informative and offered something unique. My joy...

#### Introduction to the Petfinder API with petpy

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#### Petpy v1.0 Released!

I am very excited to announce the release of Petpy v1.0! Petpy is a simple to use wrapper for the Petfinder API written in Python. The Petfinder API enables users...

#### Mathpy 0.3.0 Released!

I am excited to announce the release of mathpy 0.3.0! This release adds a ton of Excel UDFs including many new statistical and number-theoretic functions, several random number generators and...

#### Combined Linear Congruential Generators with R

Combined linear congruential generators, as the name implies, are a type of PRNG (pseudorandom number generator) that combine two or more LCGs (linear congruential generators). The combination of two or...

#### Multiplicative Congruential Generators in R

Multiplicative congruential generators, also known as Lehmer random number generators, is a type of linear congruential generator for generating pseudorandom numbers in $U(0, 1)$. The multiplicative congruential generator, often abbreviated...

#### Mathpy 0.2.0 Released!

My Python library, mathpy, a collection of mathematical and statistical functions with Excel integration, has a new release! Version 0.2.0 introduces a ton of additional mathematical and statistical functions have...

#### Linear Congruential Generator in R

A Linear congruential generator (LCG) is a class of pseudorandom number generator (PRNG) algorithms used for generating sequences of random-like numbers. The generation of random numbers plays a large role...

#### Simpson’s Rule for Approximating Definite Integrals in R

Simpson’s rule is another closed Newton-Cotes formula for approximating integrals over an interval with equally spaced nodes. Unlike the trapezoidal rule, which employs straight lines to approximate a definite integral,...

#### The Trapezoidal Rule of Numerical Integration in R

The Trapezoidal Rule is another of Closed Newton-Cotes formulas for approximating the definite integral of a function. The trapezoidal rule is so named due to the area approximated under the...

#### Numerical Differentiation with Finite Differences in R

Numerical differentiation is a method of approximating the derivative of a function $f$ at particular value $x$. Often, particularly in physics and engineering, a function may be too complicated to...

#### Divided Differences Method of Polynomial Interpolation

The divided differences method is a numerical procedure for interpolating a polynomial given a set of points. Unlike Neville’s method, which is used to approximate the value of an interpolating...

#### Neville’s Method of Polynomial Interpolation

Neville’s method evaluates a polynomial that passes through a given set of $x$ and $y$ points for a particular $x$ value using the Newton polynomial form. Neville’s method is similar...

#### Lagrangian Polynomial Interpolation with R

Polynomial interpolation is the method of determining a polynomial that fits a set of given points. There are several approaches to polynomial interpolation, of which one of the most well...

#### Set Theory Arbitrary Union and Intersection Operations with R

The union and intersection set operations were introduced in a previous post using two sets, $a$ and $b$. These set operations can be generalized to accept any number of sets. Arbitrary...

#### Set Operations Unions and Intersections in R

The set operations of unions and intersections should ring a bell for those who’ve worked with relational databases and Venn Diagrams. The ‘union’ of two of sets $A$ and $B$...

#### Introduction to Set Theory and Sets with R

Sets define a ‘collection’ of objects, or things typically referred to as ‘elements’ or ‘members.’ The concept of sets arises naturally when dealing with any collection of objects, whether it...

#### QR Decomposition with Householder Reflections

The more common approach to QR decomposition is employing Householder reflections rather than utilizing Gram-Schmidt. In practice, the Gram-Schmidt procedure is not recommended as it can lead to cancellation that...

#### QR Decomposition with the Gram-Schmidt Algorithm

QR decomposition is another technique for decomposing a matrix into a form that is easier to work with in further applications. The QR decomposition technique decomposes a square or rectangular...

#### Hierarchical Clustering Nearest Neighbors Algorithm in R

Hierarchical clustering is a widely used and popular tool in statistics and data mining for grouping data into ‘clusters’ that exposes similarities or dissimilarities in the data. There are many...

#### Iterated Principal Factor Method of Factor Analysis with R

The iterated principal factor method is an extension of the principal factor method that seeks improved estimates of the communality. As seen in the previous post on the principal factor...

#### Factor Analysis with the Principal Factor Method and R

As discussed in a previous post on the principal component method of factor analysis, the $\hat{\Psi}$ term in the estimated covariance matrix $S$, $S = \hat{\Lambda} \hat{\Lambda}' + \hat{\Psi}$, was...

#### Factor Analysis with the Principal Component Method Part Two

In the first post on factor analysis, we examined computing the estimated covariance matrix $S$ of the rootstock data and proceeded to find two factors that fit most of the...

#### LDA for Classification into Several Groups

Similar to the two-group linear discriminant analysis for classification case, LDA for classification into several groups seeks to find the mean vector that the new observation $y$ is closest to...

#### Quadratic Discriminant Analysis of Two Groups

As mentioned in the post on classification with linear discriminant analysis, LDA assumes the groups in question have equal covariance matrices $(\Sigma_1 = \Sigma_2 = \cdots = \Sigma_k)$. Therefore, often...

#### Classification with Linear Discriminant Analysis

Classification with linear discriminant analysis is a common approach to predicting class membership of observations. A previous post explored the descriptive aspect of linear discriminant analysis with data collected on...

#### Discriminant Analysis of Several Groups

Discriminant analysis is also applicable in the case of more than two groups. In the first post on discriminant analysis, there was only one linear discriminant function as the number...

#### MANOVA Test Statistics with R

Multiple tests of significance can be employed when performing MANOVA. The most well known and widely used MANOVA test statistics are Wilk’s $\Lambda$, Pillai, Lawley-Hotelling, and Roy’s test. Unlike ANOVA...

#### Multiple Analysis of Variance (MANOVA)

MANOVA, or Multiple Analysis of Variance, is an extension of Analysis of Variance (ANOVA) to several dependent variables. The approach to MANOVA is similar to ANOVA in many regards and...

#### Discriminant Analysis for Group Separation in R

The term ‘discriminant analysis’ is often used interchangeably to represent two different objectives. These objectives of discriminant analysis are: Description of group separation. Linear combinations of variables, known as discriminant functions,...

#### Image Compression with Singular Value Decomposition

As mentioned in a previous post, image compression with singular value decomposition is a frequently occurring application of the method. The image is treated as a matrix of pixels with...

#### Singular Value Decomposition in R

Following from a previous post on the Cholesky decomposition of a matrix, I wanted to explore another often used decomposition method known as Singular Value Decomposition, also called SVD. SVD...

#### How to Calculate Eigenvalues and Eigenvectors Manually and with R

Eigenvalues and eigenvectors prominently appear in many statistical and other computational fields that require transformations of linear systems or are interested in the evolution of systems from an initial point....

#### The Matrix Trace in R and Some Properties of the Trace

Although comparatively straightforward in nature, the matrix trace has many properties related to other matrix operations and often appears in statistical methods such as maximum likelihood estimation of the covariance...

#### Cholesky Decomposition of a Positive-Definite Matrix

Cholesky decomposition, also known as Cholesky factorization, is a method of decomposing a positive-definite matrix. A positive-definite matrix is defined as a symmetric matrix where for all possible vectors $x$,...

#### The Bisection Method of Root-Finding with R

The bisection method is another approach to finding the root of a continuous function $f(x)$ on an interval $[a, b]$. The method takes advantage of a corollary of the intermediate...

#### The Secant Method Root-Finding Algorithm in R

The secant method for finding roots of nonlinear equations is a common and popular variation of the Newton-Raphson method that has been used for several millennia before the invention of...

#### The Newton-Raphson Root-Finding Algorithm in R

The Newton-Raphson method is an approach for finding the roots of nonlinear equations and is one of the most common root-finding algorithms due to its relative simplicity and speed. The...

#### Using R and SQL to Analyze United States Electric Utilities

R and SQL make excellent complements for analyzing data due to their respective strengths. The sqldf package provides an interface for working with SQL in R by querying data from...

#### Simultaneous Confidence Intervals with Bonferroni and Working-Hotelling Procedures

In a previous post on multiple regression with two predictor variables, the relationship between the number of products and the distance traveled on total delivery time was examined in the...

#### How to Calculate the Inverse Matrix for 2×2 and 3×3 Matrices

Inverses of Numbers and Matrices The inverse of a number is its reciprocal. For example, the inverse of 8 is $\frac{1}{8}$, the inverse of 20 is $\frac{1}{20}$ and so on. Therefore,...

#### Multiple Regression Matrix Calculation in the Two Predictor Case

Multiple regression is a widely utilized method due to its relatively straightforward nature and power of fitting linear relationships. The concepts explored in a previous post on simple regression apply...

#### Analyzing the Consumer Complaints Database with SQL and Pandas

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#### Linear Regression through the Origin

The linear regression models examined so far have always included a constant that represents the point the regression line crosses the y-axis, called the intercept. However, there are some cases...

#### Linear Regression Confidence and Prediction Intervals

In a previous example, linear regression was examined through the simple regression setting, i.e., one independent variable. Fitting a linear model allows one to answer questions such as: What is the...

#### Simple Linear Regression Models with R

Linear regression is a widely used technique to model the association between a dependent variable and one or more independent variables. In the Simple Linear Regression setting, which is what...

#### Games-Howell Test for Post-Hoc Analysis

The Games-Howell post-hoc test is another nonparametric approach to compare combinations of groups or treatments. Although rather similar to Tukey’s test in its formulation, the Games-Howell test does not assume...

#### Spearman’s Rank Correlation Coefficient

In a previous example, linear correlation was examined with Pearson’s $r$. The cars dataset that was examined exhibited a strong linear relationship, and thus Pearson’s correlation was a good candidate...

#### Measuring Variable Relationships with Pearson’s Correlation Coefficient

Introduction to Correlation Often of interest in analyzing data is measuring the strength of association between two variables. This allows the analyst to answer such questions as “Does X predict Y?”...

#### Post-Hoc Analysis with Tukey’s Test

In a previous example, ANOVA (Analysis of Variance) was performed to test a hypothesis concerning more than two groups. Although ANOVA is a powerful and useful parametric approach to analyzing...

#### More Post-Hoc Testing with Kruskal-Wallis

The Kruskal-Wallis test extends the Mann-Whitney-Wilcoxon Rank Sum test for more than two groups. The test is nonparametric similar to the Mann-Whitney test and as such does not assume the...

#### ANOVA for Comparing More than Two Groups

ANOVA, or Analysis of Variance, is a commonly used approach to testing a hypothesis when dealing with two or more groups. One-way ANOVA, which is what will be explored in...

#### Measuring Cabbages with Mann-Whitney

In previous examples, hypothesis testing with two independent samples drawn from normally distributed populations was explored. Often, however, data is not normally distributed, which causes the t-test to output incorrect...

#### Estimating Professor Salaries with Confidence Intervals

Introduction Estimating with confidence intervals is another form of hypothesis testing that is often preferred over standard hypothesis testing such as what was explored in the previous post. A primary reason...

#### Two-Sample Hypothesis Testing with University Professor Salaries

Introduction to Hypothesis Testing Classical hypothesis testing is concerned with testing two statements, the null, and alternative hypothesis. The null hypothesis is believed to be true while the alternative hypothesis is...

#### Predicting Extramarital Affairs with Decision Trees and R

In this example, we'll build classification decision trees to analyze if a particular individual will commit an affair on their partner based on demographics and other data. Getting Started Start by loading...

### My Witcher 3 Balance Mod is Live!

#### Use IPython Notebooks as WordPress Blog Posts

The IPython Notebook is a useful tool for creating reproducible research and sharing work with other users. The notebook's ability to combine code, text, plots, images, math and even web...

#### Display Custom IPython Notebook Themes in nbviewer

Nbviewer is a wonderful way to share IPython Notebooks as it allows users to enter a URL of the notebook location, or a Github repo link, and statically displays the...

#### Export IPython Notebook with Custom CSS Using nbconvert

In the previous post, a new Ipython Notebook theme was created with custom CSS. In this post, we will explore how to export notebooks using the nbconvert tool with custom...

#### Create a Custom IPython Notebook Theme with CSS

The IPython Notebook is a powerful tool for doing quick and reproducible research and analysis by combining code, text, math, plots and even web pages into a single environment. It's...

#### Store New York Times API Data in Amazon S3 with Python

[raw] function resizeIframe(ifrm) { ifrm.style.height = ifrm.contentWindow.document.body.scrollHeight + 'px'; // Setting the width here, or setting overflowX to...

#### Get Started with Amazon Web Services Simple Storage Service (S3)

AWS, or Amazon Web Services, is a cloud-computing platform with a variety of different products and services, ranging from data storage, computing and machine learning. Some of the more popular...

#### Using Logistic Regression to Model and Predict Category Values

Introduction In this post, we will learn more about using logistic regression to classify and predict categorical values. An introduction to classification and logistic regression will be discussed in order to...

### Merge First Worksheets from all Excel Workbooks in Folder

#### Installing and Getting Started with Python for Windows

Python can be a chore to install and test on Windows systems for new users due to the need to deal with system paths and other settings that can get...

#### ARIMA Forecasting with Excel and R

Hello! Today I am going to walk you through an introduction to the ARIMA model and its components, as well as a brief explanation of the Box-Jenkins method of how...

#### Linear Regression with R Example

Linear regression models find relationships between a dependent variable, often designated y, and one or more dependent variables often denoted x. Linear regression has two primary functions and has a...

#### Linear Regression in Excel with Python

Expanding on my previous post about xlwings, I wanted to see if I could create a method in Excel to perform linear regression using statsmodels, a Python package for statistical...

#### Data Analysis with Python in Excel

I recently discovered xlwings, a package that allows you to work interactively with Excel and Python. You can read and write Excel from an IPython notebook, and it works perfectly...

#### Introduction to Github

During my free time at work, I like to work on Excel and other projects that help the team. I've recently fallen in love with Github and decided to start...

#### Count Unique Values Using Excel

Hey, everyone! Today I'll walk through how to find non-destructively unique values in your data. I say 'non-destructively' because I notice it is common for people looking for unique values...

#### Parsing Text from Cells in Excel

What up Excel-party people! Coming at you with something that I find pretty useful and applies to a large number of situations, Parsing Words in Text Strings and Cells. Originally, the...

#### Excel Sumproduct Function and Applications

Today I'm going to introduce you to the awesome function that is SUMPRODUCT. You can tell I'm excited as this is one of my go to functions due to its...

#### Excel Vlookup Wildcards and Examples

Alrighty, imagine a situation where you have a set of data but aren't too familiar with it. Maybe it was handed off or whatever, and you need to figure it...

#### Excel’s Index + Match: An Alternative to Vlookup

Everyone knows VLOOKUP is an excellent formula and is useful in a wide variety of cases. However, there are some limitations to the function. The biggest one is VLOOKUP can...