Logistic Regression Defaults and sklearn

Giovanni Lanzani shares some thoughts on scikit-learn defaults for Logistic Regression:

If you read the post, you can see that the biggest problem with the choice is that, unless your data is regularized, you will train a model that probably under performs: you are unnecessarily penalizing it by making it learn less than what it could from the data.

The second problem with the default behavior of LogisticRegression is about choosing a regularization constant that is — in effect — a magic number (equal to 1.0). This hides the fact that the regularization constant should be tuned by hyperparameter search, and not set in advance without knowing how the data and problem looks like.

Knowledge is power. Also read the post Giovanni links to in order to learn more about the issue.

Python and R Data Reshaping

John Mount takes us through a couple of data shaping packages:

The advantages of data_algebra and cdata are:

– The user specifies their desired transform declaratively by example and in data. What one does is: work an example, and then write down what you want (we have a tutorial on this here).
– The transform systems can print what a transform is going to do. This makes reasoning about data transforms much easier.
– The transforms, as they themselves are written as data, can be easily shared between systems (such as R and Python).

Let’s re-work a small R cdata example, using the Python package data_algebra.

Click through for the example.

Develop BDC PySpark Jobs in Visual Studio Code

Jenny Jiang announces a new capability in Visual Studio Code:

With the Visual Studio Code extension, you can enjoy native Python programming experiences such as linting, debugging support, language service, and so on. You can run current linerun selected lines of code, or run all for your PY file. You can import and export a .ipynb notebook and perform a notebook like query including Run Cell, Run Above, or Run Below. You can also enjoy a notebook like interactive experience that includes your source code and markdown comments along with the running results and output. You can remove the unneeded sections, enter comments, or type additional code in the interactive results window. Moreover, you can visualize your results in a graphic format through a matplotlib like Jupyter Notebook. The integration with SQL Server 2019 Big Data Clusters empowers you to quickly submit a PySpark batch job to the big data cluster and monitor job progress.

This is rather useful for developers, though I greatly prefer the Azure Data Studio notebook interface.

Eliminating Tail Calls in Python

Kevin Feasel

2019-08-29

Python

John Mount shows how you can eliminate tail calls in Python:

I was working through Kyle Miller‘s excellent note: “Tail call recursion in Python”, and decided to experiment with variations of the techniques.

The idea is: one may want to eliminate use of the Python language call-stack in the case of a “tail calls” (a function call where the result is not used by the calling function, but instead immediately returned). Tail call elimination can both speed up programs, and cut down on the overhead of maintaining intermediate stack frames and environments that will never be used again.

Click through for John’s riff on the topic.

The Basics of Apache Airflow

Divyansh Jain explains what Apache Airflow is and takes us through a sample solution:

Airflow is a platform to programmatically author, schedule & monitor workflows or data pipelines. These functions achieved with Directed Acyclic Graphs (DAG) of the tasks. It is an open-source and still in the incubator stage. It was initialized in 2014 under the umbrella of Airbnb since then it got an excellent reputation with approximately 800 contributors on GitHub and 13000 stars. The main functions of Apache Airflow is to schedule workflow, monitor and author.

It’s another interesting product in the Hadoop ecosystem and has additional appeal outside of that space.

Python versus R (Again)

Alex Woodie looks at whether Python is dominating R in the data science space:

There is some evidence that Python’s popularity is hurting R usage. According to the TIOBE Index, Python is currently the third most popular language in the world, behind perennial heavyweights Java and C. From August 2018 to August 2019, Python usage surged by more than 3% to achieve a 10% rating (TIOBE’s proprietary metric that primarily measures search activity), easily the biggest gain among the 20 most popular languages.

R, by contrast, has not fared well lately on the TIOBE Index, where it dropped from 8th place in January 2018 to become the 20th most popular language today, behind Perl, Swift, and Go. At its peak in January 2018, R had a popularity rating of about 2.6%. But today it’s down to 0.8%, according to the TIOBE index.

I’ll say that rumors of R’s demise are premature.

Microsoft ML Server 9.4

Kevin Feasel

2019-07-31

Python, R

Jeroen Ter Heerdt announces Microsoft Machine Learning Server 9.4:

Today we’re excited to announce our latest Microsoft Machine Learning Server 9.4 release, which addresses popular customer requests as well as developments in the R and Python community.

Microsoft Machine Learning Server is your flexible enterprise platform for analyzing data at scale, building intelligent apps, and discovering valuable insights across your business with full support for Python and R. Machine Learning Server meets the needs of all constituents of the process – from data engineers and data scientists to line-of-business programmers and IT professionals. It offers a choice of languages and features and algorithmic innovation that brings the best of open source and proprietary worlds together.

This is the best way to bind new versions of R and Python to your SQL Server ML Services installation.

Building an Image Classifier with PyTorch

Rogier van der Geer shows how you can use PyTorch to build out a Convolutional Neural Network for image classification:

The tool that we are going to use to make a classifier is called a convolutional neural network, or CNN. You can find a great explanation of what these are right here on wikipedia.

But we are not going to fully train one ourselves: that would take way more time than I would be willing to spend. Instead, we are going to do transfer learning, where we take a pre-trained CNN and replace only the last layer by a layer of our own. Then we only need to train that single layer, as all the other layers already have weights that are quite sensible. Here we exploit the fact that the images we are interested in have a lot of the same properties as those images that the original network was trained on. You can find a great explanation of transfer learning here.

Read on for a detailed example.

A Quick Keras Example

Shubham Dangare takes us through a quick example using Keras and TensorFlow in Python:

Keras is a high-level neural networks API, written in Python and capable of running on top of Tensorflow, CNTK  or Theano. It was developed with a focus on enabling fast experimentation. In this blog, we are going to cover one small case study for fashion mnist.

Fashion-MNIST is a dataset of Zalando’s article images—consisting of a training set of 60,000 examples and a test set of 10,000 examples. Each example is a 28×28 grayscale image, associated with a label from 10 classes. Zalando intends Fashion-MNIST to serve as a direct drop-in replacement for the original MNIST dataset for benchmarking machine learning algorithms. It shares the same image size and structure of training and testing splits.

The end result wasn’t that great, but Shubham was using a sequential model rather than a convolutional neural network, so you can probably take this as a starting point and improve upon it.

ML Services and Injectable Code

Grant Fritchey looks at sp_execute_external_script for potential SQL injection vulnerabilities:

The sharp eyed will see that the data set is defined by SQL. So, does that suffer from injection attacks? Short answer is no. If there was more than one result set within the Python code, it’s going to error out. So you’re protected there.

This is important, because the data set query can be defined with parameters. You can pass values to those parameters, heck, you’re likely to pass values to those parameters, from the external query or procedure. So, is that an attack vector?

No.

Another factor is that you need explicitly to grant EXECUTE ANY EXTERNAL SCRIPT rights to non-sysadmin, non-db_owner users, meaning a non-privileged user can’t execute external scripts at all. You can also limit the executing service account

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