Practical Business Python

Taking care of business, one python script at a time

Mon 06 February 2017

Guide to Encoding Categorical Values in Python

Posted by Chris Moffitt in articles   

In many practical Data Science activities, the data set will contain categorical variables. These variables are typically stored as text values which represent various traits. Some examples include color (“Red”, “Yellow”, “Blue”), size (“Small”, “Medium”, “Large”) or geographic designations (State or Country). Regardless of what the value is used for, the challenge is determining how to use this data in the analysis. Many machine learning algorithms can support categorical values without further manipulation but there are many more algorithms that do not. Therefore, the analyst is faced with the challenge of figuring out how to turn these text attributes into numerical values for further processing.

As with many other aspects of the Data Science world, there is no single answer on how to approach this problem. Each approach has trade-offs and has potential impact on the outcome of the analysis. Fortunately, the python tools of pandas and scikit-learn provide several approaches that can be applied to transform the categorical data into suitable numeric values. This article will be a survey of some of the various common (and a few more complex) approaches in the hope that it will help others apply these techniques to their real world problems.

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Mon 19 December 2016

Building a Financial Model with Pandas - Version 2

Posted by Chris Moffitt in articles   

In my last article, I discussed building a financial model in pandas that could be used for multiple amortization scenarios. Unfortunately, I realized that I made a mistake in that approach so I had to rethink how to solve the problem. Thanks to the help of several individuals, I have a new solution that resolves the issues and produces the correct results.

In addition to posting the updated solution, I have taken this article as an opportunity to take a step back and examine what I should have done differently in approaching the original problem. While it is never fun to make a mistake in front of thousands of people, I’ll try to swallow my pride and learn from it.

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Mon 21 November 2016

Building a Financial Model with Pandas

Posted by Chris Moffitt in articles   

In my previous articles, I have discussed how to use pandas as a replacement for Excel when it comes to data wrangling. In many cases, a python + pandas solution is superior to the highly manual processes many people use for manipulating data in Excel. However, Excel is used for many scenarios in a business environment - not just data wrangling. This specific post will discuss how to do financial modeling in pandas instead of Excel. For this example, I will build a simple amortization table in pandas and show how to model various outcomes.

In some ways, building the model is easier in Excel (there are many examples just a google search away). However, as an exercise in learning about pandas, it is useful because it forces you to think about how to use pandas strengths to solve a problem in a way different from the Excel solution. In my opinion the solution is more powerful because you can build on it to run multiple scenarios, easily chart various outcomes and focus on aggregating the data in a way most useful for your needs.

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Tue 06 September 2016

Creating Pandas DataFrames from Lists and Dictionaries

Posted by Chris Moffitt in articles   

Whenever I am doing analysis with pandas my first goal is to get data into a panda’s DataFrame using one of the many available options. For the vast majority of instances, I use read_excel, read_csv, or read_sql.

However, there are instances when I just have a few lines of data or some calculations that I want to include in my analysis. In these cases it is helpful to know how to create DataFrames from standard python data structures such as lists or dictionaries. The basic process is not difficult but because there are several different options it is helpful to understand how each works. I can never remember whether I should use from_dict, from_records, from_items or the default DataFrame constructor. Normally, through some trial and error, I figure it out. Since it is still confusing to me, I thought I would walk through several examples below to clarify the different approaches. At the end of the article, I briefly show how this can be useful when generating Excel reports.

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Wed 06 April 2016

Interactive Data Analysis with Python and Excel

Posted by Chris Moffitt in articles   

I have written several times about the usefulness of pandas as a data manipulation/wrangling tool and how it can be used to efficiently move data to and from Excel. There are cases, however, where you need an interactive environment for data analysis and trying to pull that together in pure python, in a user-friendly manner would be difficult. This article will discuss how to use xlwings to tie Excel, Python and pandas together to build a data analysis tool that pulls information from an external database, manipulates it and presents it to the user in a familiar spreadsheet format.

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Tue 26 January 2016

Learn More About Pandas By Building and Using a Weighted Average Function

Posted by Chris Moffitt in articles   

Pandas includes multiple built in functions such as sum, mean, max, min, etc. that you can apply to a DataFrame or grouped data. However, building and using your own function is a good way to learn more about how pandas works and can increase your productivity with data wrangling and analysis.

The weighted average is a good example use case because it is easy to understand but useful formula that is not included in pandas. I find that it can be more intuitive than a simple average when looking at certain collections of data. Building a weighted average function in pandas is relatively simple but can be incredibly useful when combined with other pandas functions such as groupby.

This article will discuss the basics of why you might choose to use a weighted average to look at your data then walk through how to build and use this function in pandas. The basic principles shown in this article will be helpful for building more complex analysis in pandas and should also be helpful in understanding how to work with grouped data in pandas.

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Mon 07 December 2015

Creating Advanced Excel Workbooks with Python

Posted by Chris Moffitt in articles   

I have written several articles about using python and pandas to manipulate data and create useful Excel output. In my experience, no matter how strong the python tools are, there are times when you need to rely on Excel as the vehicle to communicate your message or further analyze the data. This article will walk through some additional improvements you can make to your Excel-based output by:

  • Adding Excel tables with XlsxWriter

  • Inserting custom VBA into your Excel file

  • Using COM for merging multiple Excel worksheets

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Mon 26 October 2015

Pandas 0.17 Release and Other Notes

Posted by Chris Moffitt in articles   

As many of you know, pandas released version 0.17.0 on October 9th. In typical pandas fashion there are a bunch of updates, bug fixes and new features which I encourage you to read all about here. I do not plan to go through all of the changes but there are a couple of key things that I think will be useful to me in my daily work that I will explore briefly in this article. In addition, I am including a couple of other tips and tricks for pandas that I use on a frequent basis and hope will be useful to you.

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Mon 14 September 2015

Adding a Simple GUI to Your Pandas Script

Posted by Chris Moffitt in articles   

Using python and pandas in the business world can be a very useful alternative to the pain of manipulating Excel files. While this combination of technologies is powerful, it can be challenging to convince others to use a python script - especially when many may be intimidated by using the command line. In this article I will show an example of how to easily create an end-user-friendly GUI using the Gooey library. This interface is based on wxWindows so it looks like a “native” application on Windows, Mac and Linux. Ultimately, I believe that presenting a simple user interface to your scripts can greatly increase the adoption of python in your place of business.

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