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Category: Python

Fun with Python: Calculating Pi

Jon Fletcher implements a method of estimating the value of Pi:

This series converges to Pi, the more terms that are added to the series, the closer the value is to Pi.
For the proof on why this series converges to Pi – https://proofwiki.org/wiki/Leibniz’s_Formula_for_Pi
There are several points to note about the series:

– It’s infinite, we need to find a way to continue adding term after term.
– The denominator of the fraction increases by 2 every term.
– The terms alternate between positive and negative.

Click through for the implementation of the formula in Python. And what you should do if you really need to reference Pi in your Python code.

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Distributed Model Training with Dask and SciKit-Learn

Matthieu Lamairesse shows us how we can use Dask to perform distributed ML model training:

Dask is an open-source parallel computing framework written natively in Python (initially released 2014). It has a significant following and support largely due to its good integration with the popular Python ML ecosystem triumvirate that is NumPy, Pandas and Scikit-learn. 

Why Dask over other distributed machine learning frameworks? 

In the context of this article it’s about Dask’s tight integration with Sckit-learn’s JobLib parallel computing library that allows us to distribute Scikit-learn code with (almost) no code change, making it a very interesting framework to accelerate ML training. 

Click through for an interesting article and an example of using this on Cloudera’s ML platform.

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Using Python to Pivot Data in SQL Server

Rajendra Gupta shows a few ways to pivot data using Python:

We can use groupby and lambda functions as well in the Python scripts for Pivot tables. For this example, I have a data set of a few states of India and their cities in a SQL table.

We need a pivot table from this data. In the output, it should list all cities for a state in a column; it should use || as a city name separator.

This is an unorthodox but interesting use of Machine Learning Services.

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Python Cross-Validation

John Mount has some advice if you’re doing cross-validation in Python:

Here is a quick, simple, and important tip for doing machine learning, data science, or statistics in Python: don’t use the default cross validation settings. The default can default to a deterministic, and even ordered split, which is not in general what one wants or expects from a statistical point of view. From a software engineering point of view the defaults may be sensible as since they don’t touch the pseudo-random number generator they are repeatable, deterministic, and side-effect free.

This issue falls under “read the manual”, but it is always frustrating when the defaults are not sufficiently generous.

Click through to see the problem and how you can fix it.

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Machine Learning through Counterfactuals

Amit Sharma announces a new library:

Consider a person who applies for a loan with a financial company, but their application is rejected by a machine learning algorithm used to determine who receives a loan from the company. How would you explain the decision made by the algorithm to this person? One option is to provide them with a list of features that contributed to the algorithm’s decision, such as income and credit score. Many of the current explanation methods provide this information by either analyzing the algorithm’s properties or approximating it with a simpler, interpretable model.

However, these explanations do not help this person decide what to do next to increase their chances of getting the loan in the future. In particular, changing the most important features for prediction may not actually change the decision, and in some cases, important features may be impossible to change, such as age. A similar argument applies when algorithms are used to support decision-makers in scenarios such as screening job applicants, deciding health insurance, or disbursing government aid.

This has the potential to be a great library. One of the issues with machine learning as it stands today is that you can get an answer, but to understand how to change the answer requires having a human understand the model. This looks like a good first step. It’s only available in Python.

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Choosing Categorical Features with Python

Mesfin Gebeyaw shows how to use Multiple Correspondence Analysis to filter categorical variables for an analysis:

A general guide to interpreting the multiple correspondence analysis plot shown above for business insights would be to make a note as to how close input categorical features are to the target variable customer churn and to each other. For instance, senior citizens, customers with fiber optic internet service, those with month to month contractual agreements, and single customers or customers with no dependents are being related to a short tenure with the company and a propensity of high risk to churn. On the other hand, customers with more than a year contract, those with DSL internet service, younger customers, customers with multiple lines are being related to a long tenure with the company and a higher tendency to stay with company.

Read the whole thing.

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Data Visualization in R and Python

Michelle Golchert contrasts libraries for visualizing data in R and Python:

Unlike R, Python – as a “general-purpose” programming language – does not include data visualization tools by default. However, Python also provides many libraries for this purpose, such as Matplotlib and Seaborn.

Python now also offers numerous packages (like plotnine and ggpy) which are equivalents of ggplot2 in R, and allow you to create plots in Python according to the same “Grammar of Graphics” principle.

This is an area where I think R has the upper hand at most levels: it’s easier to get started plotting with R (thanks to the built-in plots), it’s easier to do “intermediate-quality” plots (stuff you would use in an internal presentation), and you tend to have more control when building professional-quality plots. You can certainly create beautiful visuals in both languages, though.

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Schiphol Takeoff: Low-Code Automated Deployment

Tim van Cann and Daniel van der Ende have an open source project for automatic deployment on Azure:

To give a bit more insight into why we built Schiphol Takeoff, it’s good to take a look at an example use case. This use case ties a number of components together:

– Data arrives in a (near) real-time stream on an Azure Eventhub.
– A Spark job running on Databricks consumes this data from Eventhub, processes the data, and outputs predictions.
– A REST API is running on Azure Kubernetes Service, which exposes the predictions made by the Spark job.

Conceptually, this is not a very complex setup. However, there are quite a few components involved:

– Azure Eventhub
– Azure Databricks
– Azure Kubernetes Service

Each of these individually has some form of automation, but there is no unified way of coordinating and orchestrating deployment of the code to all at the same time. If, for example, you were to change the name of the consumer group for Azure Eventhub, you could script that. However, you’d also need to manually update your Spark job running on Databricks to ensure it could still consume the data.

This looks pretty nice. I’ll need to dive into it some more.

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