You can access the course materials quickly from

https://ayoubbagheri.nl/applied_tm/

• Text data are everywhere!
• A lot of world’s data are in the format of unstructured text
• This course teaches
  • text mining techniques
  • using Python
  • on a variety of applications
  • in many domains.

• What is your experience level with Python?

• Which Python IDE do you mostly use? If you use more than one environment fill in the other text boxes.

• How familiar are you with Google Colab? (1: limited to 5: expert)

• Latest: Python 3.11.4

• Follow the tutorial on Python in Google Colab for the Applied Text Mining course: link

• Python For Beginners

  • https://www.python.org/about/gettingstarted/

• The Python Language Reference

  • https://docs.python.org/3/reference/

• Python 3.11.4 documentation

  • https://docs.python.org/3/

• Colaboratory, or “Colab” for short, allows you to write and execute Python in your browser, with

  • Zero configuration required
  • Free access to GPUs
  • Easy sharing

• [Intro](https://colab.research.google.com/notebooks/intro.ipynb)

• Cheat-sheet for Google Colab

• Keyboard shortcuts:

• Different things can mean more or less the same (“data science” vs. “statistics”)
• Context dependency (“You have very nice shoes”);
• Same words with different meanings (“to sanction”, “bank”);
• Lexical ambiguity (“we saw her duck”)
• Irony, sarcasm (“That’s just what I needed today!”, “Great!”, “Well, what a surprise.”)
• Figurative language (“He has a heart of stone”)
• Negation (“not good” vs. “good”), spelling variations, jargon, abbreviations
• All the above are different over languages, 99% of work is on English!

• “the discovery by computer of new, previously unknown information, by automatically extracting information from different written resources” Hearst (1999)

• Text mining is about looking for patterns in text, in a similar way that data mining can be loosely described as looking for patterns in data.

• Text mining describes a set of linguistic, statistical, and machine learning techniques that model and structure the information content of textual sources. (Wikipedia)

• We won’t solve linguistics …
• In spite of the problems, text mining can be quite effective!

• Text classification
• Text clustering
• Sentiment analysis
• Feature selection
• Topic modelling
• Responsible text mining
• Text summarization

• is an approach for cleaning and noise removal of text data.
• brings your text into a form that is analyzable for your task.
• transforms text into a more digestible form so that machine learning algorithms can perform better.

• Tokenization (“text”, “ming”, “is”, “the”, “best” , “!”)
• Stemming (“lungs”→“lung”) or Lemmatization (“were”→“is”)
• Lowercasing (“Disease”→“disease”)
• Stopword removal (“text ming is best!”)
• Punctuation removal (“text ming is the best”)
• Number removal (“I42”→“I”)
• Spell correction (“hart”→“heart”)

Not all of these are appropriate at all times!

• Split text into words and sentences

• N-grams: a contiguous sequence of N tokens from a given piece of text

  • E.g., ‘Text mining is to identify useful information.’

  • Bigrams: ‘text_mining’, ‘mining_is’, ‘is_to’, ‘to_identify’, ‘identify_useful’, ‘useful_information’, ‘information_.’

• Pros: capture local dependency and order

• Cons: increase the vocabulary size

• Annotate each word in a sentence with a part-of-speech.

• Useful for subsequent syntactic parsing and word sense disambiguation.

• Text is “unstructured data”
• How do we get to something structured that we can compute with?
• Text must be represented somehow
• Represent the text as something that makes sense to a computer

• Represent by a string?

  • No semantic meaning

• Represent by a list of sentences?

  • Sentence is just like a short document (recursive definition)

• Represent by a vector?

  • A vector is an ordered finite list of numbers.

• A vector space is a collection of vectors

• Represent documents by concept vectors

  • Each concept defines one dimension

  • k concepts define a high-dimensional space

  • Element of vector corresponds to concept weight

• Distance between the vectors in this concept space

  • Relationship among documents

• The process of converting text into numbers is called Vectorization

• Terms are generic features that can be extracted from text

• Typically, terms are single words, keywords, n-grams, or phrases

• Documents are represented as vectors of terms

• Each dimension (concept) corresponds to a separate term

\[d = (w_1, ..., w_n)\]

• All documents are projected into this concept space

• Terms are words (more generally we can use n-grams)
• Weights are number of occurrences of the terms in the document
  • Binary
  • Term Frequency (TF)
  • Term Frequency inverse Document Frequency (TFiDF)

• Doc1: Text mining is to identify useful information.

• Doc2: Useful information is mined from text.

• Doc3: Apple is delicious.

• Idea: a term is more important if it occurs more frequently in a document

• TF formulas

  • Let \(t(c,d)\) be the frequency count of term \(t\) in doc \(d\)

  • Raw TF: \(tf(t,d) = c(t,d)\)

• Idea: a term is more discriminative if it occurs a lot but only in fewer documents

Let \(n_{d,t}\) denote the number of times the \(t\)-th term appears in the \(d\)-th document.

\[TF_{d,t} = \frac{n_{d,t}}{\sum_i{n_{d,i}}}\] Let \(N\) denote the number of documents annd \(N_t\) denote the number of documents containing the \(t\)-th term.

\[IDF_t = log(\frac{N}{N_t})\] TFiDF weight:

\[w_{d,t} = TF_{d,t} \cdot IDF_t\]

• Euclidean distance

  \(dist(d_i, d_j) = \sqrt{\sum_{t\in V}{[tf(t,d_i)idf(t) - tf(t, d_j)idf(t)]^2}}\)

  • Longer documents will be penalized by the extra words

  • We care more about how these two vectors are overlapped

• Cosine similarity

  • Angle between two vectors:

    \(cosine(d_i, d_j) = \frac{V_{d_i}^TV_{d_j}}{|V_{d_i}|_2 \times |V_{d_j}|_2}\) ← TF-IDF vector

  • Documents are normalized by length

• Text classification

• Text data are everywhere!
• Language is hard!
• The basic problem of text mining is that text is not a neat data set
• Solution: text pre-processing & VSM