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What am I doing here? The story so far

As you might know if you have read our blog for more than a year, a few years ago, I bought a flat in Paris. If you don't know, the real estate market in Paris is expensive but despite that, it is so tight that a good flat at a correct price can be for sale for less than a day.

Obviously, you have to take a decision quite fast, and considering the prices, you have to trust your decision. Of course, to trust your decision, you have to take your time, study the market, make some visits etc This process can be quite long (in my case it took a year between the time I decided that I wanted to buy a flat and the time I actually commited to buying my current flat), and even spending a lot of time will never allow you to have a perfect understanding of the market. What if there was a way to do that very quickly and with a better accuracy than with the standard process?

As you might also know if you are one of our regular readers, I tried to solve this problem with Machine Learning, using an end-to-end software called Dataiku. In a first blog post, we learned how to make a basic use of Dataiku, and discovered that just knowing how to click on a few buttons wasn't quite enough: you had to bring some sense in your data and in the training algorithm, or you would find absurd results.

In a second entry, we studied a bit more the data, tweaked a few parameters and values in Dataiku's algorithms and trained a new model. This yielded a much better result, and this new model was - if not accurate - at least relevant: the same flat had a higher predicted place when it was bigger or supposedly in a better neighbourhood. However, it was far from perfect and really lacked accuracy for several reasons, some of them out of our control.

However, all of this was done on one instance of Dataiku - a licensed software - on a single VM. There are multiple reasons that could push me to do things differently:

What we did very intuitively (and somewhat naively) with Dataiku was actually a quite complex pipeline that is often called ELT, for Extract, Load and Transform.

And obviously, after this ELT process, we added a step to train a model on the transformed data.

So what are we going to do to redo all of that without Dataiku's help?

When ELT becomes ELTT

Now that we know what we are going to do, let us proceed!

Before beginning, we have to properly set up our environment to be able to launch the different tools and products. Throughout this tutorial, we will show you how to do everything with CLIs. However, all these manipulations can also be done on OVHcloud's manager (GUI), in which case you won't have to configure these tools.

For all the manipulations described in the next phase of this article, we will use a Virtual Machine deployed in OVHcloud's Public Cloud that will serve as the extraction agent to download the raw data from the web and push it to S3 as well as a CLI machine to launch data processing and notebook jobs. It is a d2-4 flavor with 4GB of RAM, 2 vCores and 50 GB of local storage running Debian 10, deployed in Graveline's datacenter. During this tutorial, I run a few UNIX commands but you should easily be able to adapt them to whatever OS you use if needed. All the CLI tools specific to OVHcloud's products are available on multiple OSs.

You will also need an OVHcloud NIC (user account) as well as a Public Cloud Project created for this account with a quota high enough to deploy a GPU (if that is not the case, you will be able to deploy a notebook on CPU rather than GPU, the training phase will juste take more time). To create a Public Cloud project, you can follow these steps.

Here is a list of the CLI tools and other that we will use during this tutorial and why:

Additionally you will find commented code samples for the processing and training steps in this Github repository.

In this tutorial, we will use several object storage buckets. Since we will use the S3 API, we will call them S3 bucket, but as mentioned above, if you use OVHcloud standard Public Cloud Storage, you could also use the Swift API. However, you are restricted to only the S3 API if you use our new high-performance object storage offer, currently in Beta.

For this tutorial, we are going to create and use the following S3 buckets:

To create these buckets, use the following commands after having configured your aws CLI as explained above:

Now that you have your environment set up and your S3 buckets ready, we can begin the tutorial!

First, let us download the data files directly on Etalab's website and unzip them:

You should now have the following files in your directory, each one corresponding to the French real estate transaction of a specific year:

Now, use the S3 CLI to push these files in the relevant S3 bucket:

You should now have those 5 files in your S3 bucket:

What we just did with a small VM was ingesting data into a S3 bucket. In real-life usecases with more data, we would probably use dedicated tools to ingest the data. However, in our example with just a few GB of data coming from a public website, this does the trick.

Now that you have your raw data in place to be processed, you just have to upload the code necessary to run your data processing job. Our data processing product allows you to run Spark code written either in Java, Scala or Python. In our case, we used Pyspark on Python. Your code should consist in 3 files:

Once you have your code files, go to the folder containing them and push them on the appropriate S3 bucket:

Your bucket should now look like that:

You are now ready to launch your data processing job. The following command will allow you to launch this job on 10 executors, each with 4 vCores and 15 GB of RAM.

Note that the data processing product uses the Swift API to retrieve the code files. This is totally transparent to the user, and the fact that we used the S3 CLI to create the bucket has absolutely no impact. When the job is over, you should see the following in your transactions-ecoex-clean bucket:

Before going further, let us look at the size of the data before and after cleaning:

As you can see, with ~2.5 GB of raw data, we extracted only ~10 MB of actually useful data (only 0,4%)!! What is noteworthy here is that that you can easily imagine usecases where you need a large-scale infrastructure to ingest and process the raw data but where one or a few VMs are enough to work on the clean data. Obviously, this is more often the case when working with text/structured data than with raw sound/image/videos.

Before we start training a model, take a look at these two screenshots from OVHcloud's data processing UI to erase any doubt you have about the power of distributed computing:

In the first picture, you see the time taken for this job when launching only 1 executor- 8:35 minutes. This duration is reduced to only 2:56 minutes when launching the same job (same code etc) on 4 executors: almost 3 times faster. And since you pay-as-you go, this will only cost you ~33% more in that case for the same operation done 3 times faster- without any modification to your code, only one argument in the CLI call. Let us now use this data to train a model.

To train the model, you are going to use OVHcloud AI notebook to deploy a notebook! With the following command, you will:

In our case, we launch a notebook with only 1 GPU because the code samples we provide would not leverage several GPUs for a single job. I could adapt my code to parallelize the training phase on multiple GPUs, in which case I could launch a job with up to 4 parallel GPUs.Once this is done, just get the URL of your notebook with the following command and connect to it with your browser:

Once you're done, just get the URL of your notebook with the following command and connect to it with your browser:

You can now import the real-estate-training.ipynb file to the notebook with just a few clicks. If you don't want to import it from the computer you use to access the notebook (for example if like me you use a VM to work and have cloned the git repo on this VM and not on your computer), you can push the .ipynb file to your transactions-ecoex-clean or transactions-ecoex-model bucket and re-synchronize the bucket to your notebook while it runs by using the ovhai notebook pull-data command. You will then find the notebook file in the corresponding directory.

Once you have imported the notebook file to your notebook instance, just open it and follow the directives. If you are interested in the result but don't want to do it yourself, let's sum up what the notebook does:

Use the models built in this tutorial at your own risk

So, what can we conclude from all of this? First, even if the second model is obviously better than the first, it is still very noisy: while not far from correct on average, there is still a huge variance. Where does this variance come from?

Well, it is not easy to say. To paraphrase the finishing part of my last article:

In this article, I tried to give you a glimpse at the tools that Data Scientists commonly use to manipulate data and train models at scale, in the Cloud or on their own infrastructure:

Hopefuly, you now have a better understanding on how Machine Learning algorithms work, what their limitations are, and how Data Scientists work on data to create models.

As explained earlier, all the code used to obtain these results can be found here. Please don't hesitate to replicate what I did or adapt it to other usecases!

Solutions ArchitectatOVHCloud|+ posts

Here is the original post:
OVH Groupe : A journey into the wondrous land of Machine Learning, or Cleaning data is funnier than cleaning my flat! (Part 3) - Marketscreener.com