Sequence labelling in Python (part 1)← Back to blog
I was looking for a cool project to practice sequence labelling with Python so… there is this Mexican website called VuelaX, in it, flight offers are shown. Most of the offers follow a simple pattern: Destination - Origin - Price - Extras, while extracting this may seem easy for a regular expression, it is not as there are many patterns. It would be tough for us to cover them all.
I know it is not ideal to work in a foreign language, but bear with me, as the same techniques could be applied in your language of choice.
The idea is to create a tagger that will be able to extract this information. However, one first tag is to identify the information that we want to extract. Following the pattern described above:
- o: Origin
- d: Destination
- s: Separator token
- p: Price
- f: Flag
- n: Irrelevant token
|¡CUN a Holanda $8,885! Sin escala EE.UU||CUN||Holanda||8,885||Sin escala EE.UU|
|¡CDMX a Noruega $10,061! (Y agrega 9 noches de hotel por $7,890!)||CDMX||Noruega||10,061||Y agrega 9 noches de hotel por $7,890!|
|¡Todo México a Pisa, Toscana Italia $12,915! Sin escala EE.UU (Y por $3,975 agrega 13 noches hotel)||México||Pisa, Toscana Italia||12,915||Sin escala EE.UU (Y por $3,975 agrega 13 noches hotel)|
CRFs in Python
If you are familiar with data science, you know this is known as a sequence labelling problem. While there are various ways to approach it, in this post, I will show you one that uses a statistical model known as Conditional Random Fields. Having said that, I will not delve too much into details, so if you want to learn more about CRFs you are on your own; I will show you a practical way to use it with a Python implementation.
Getting some data
To start, I scraped the offer titles data from the page mentioned above. I will not detail how I did it since it is pretty straightforward to find a tutorial on web scraping on the web. If you don’t feel like spending some time scraping a website, I collected some data in a CSV file that you can access now here.
This tutorial will be divided into other 4 parts:
- Part-Of-Speech tagging (and getting some ground truth)
- Other feature extraction
- Conditional Random Fields with python-crfsuite
- Putting everything together
Hopefully, you will follow along and will ask some questions if you have by leaving a comment here or contacting me on twitter via @feregri_no.