Movie Review Sentiment Analysis Quiz
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Questions and Answers

After creating a Bag of Words model, what is a common next step to examine the model's features?

  • Calculate the term frequency-inverse document frequency (TF-IDF)
  • Print the counts of each word in the vocabulary. (correct)
  • Apply Principal Component Analysis (PCA) on the words.
  • Generate a word cloud to visualize the most frequent words.
  • After creating numeric features using Bag of Words and having sentiment labels, what is a typical method used for classification?

  • Singular Value Decomposition (SVD)
  • K-Means clustering.
  • Random Forest classifier. (correct)
  • Linear Regression.
  • When applying a Random Forest classifier, what impact does increasing the number of trees typically have on the model?

  • It may improve or not improve the performance, but it will increase training time. (correct)
  • It will decrease the model's accuracy.
  • It will significantly speed up the training process.
  • It will always guarantee better performance.
  • For the assignment task, how should the trained Random Forest be used with the test dataset?

    <p>Apply 'forest.predict' on the test data’s features. (A)</p> Signup and view all the answers

    When submitting the results of the Random Forest classifier prediction on the test dataset, what file format is requested?

    <p>.csv or .xlsx (C)</p> Signup and view all the answers

    What does a sentiment score of 0 indicate in the IMDB movie review dataset?

    <p>A negative review with a rating less than 5. (B)</p> Signup and view all the answers

    What is the purpose of setting quoting=3 when reading the labeled training data?

    <p>To ignore double quotes and prevent errors during reading (C)</p> Signup and view all the answers

    If a movie review in the IMDB dataset has a rating of 6, what would its corresponding sentiment score be?

    <p>1 (A)</p> Signup and view all the answers

    What is the primary purpose of using the Beautiful Soup library in the context of the movie review data?

    <p>To extract text from HTML content. (B)</p> Signup and view all the answers

    What does the delimiter='\t' argument specify when reading the labeled training data?

    <p>The file uses tab characters as separators between the fields. (B)</p> Signup and view all the answers

    Why might punctuation marks be retained in sentiment analysis, as opposed to being removed?

    <p>Punctuation can carry sentiment-related information. (C)</p> Signup and view all the answers

    In the given dataset, how many labeled movie reviews are dedicated to the training set?

    <p>25,000 (A)</p> Signup and view all the answers

    What is the primary role of the re package in data cleaning for the sentiment analysis task described in the text?

    <p>To remove punctuation and numbers from the text. (C)</p> Signup and view all the answers

    What is the primary purpose of the re.sub() function mentioned in the text?

    <p>To replace all non-alphabetic characters with spaces. (C)</p> Signup and view all the answers

    What does 'tokenization' refer to in the context of NLP, as described in the text?

    <p>Splitting text into individual words. (A)</p> Signup and view all the answers

    What is a stop word?

    <p>A frequently occurring word that typically doesn't carry much meaning. (B)</p> Signup and view all the answers

    Why is it beneficial to convert the list of stop words to a set before removing them from text?

    <p>Searching sets in Python is faster than searching lists. (B)</p> Signup and view all the answers

    In the context of cleaning text data, what is the purpose of joining words back into one paragraph after removing stop words?

    <p>To make the output more suitable for use in the Bag of Words approach. (C)</p> Signup and view all the answers

    Besides re.sub(), what other processing steps are mentioned as part of cleaning movie reviews?

    <p>Converting to lowercase, and splitting into words (Tokenization). (A)</p> Signup and view all the answers

    What does the code do after the stop word removal and other text cleaning processes?

    <p>It converts the processed word back to a paragraph string. (A)</p> Signup and view all the answers

    Why is creating a function necessary for cleaning movie review data?

    <p>To make the code reusable for cleaning multiple reviews. (D)</p> Signup and view all the answers

    What does the Bag of Words model primarily do?

    <p>It learns a vocabulary from all provided documents, then quantifies word occurrences in each. (C)</p> Signup and view all the answers

    In the example given, what is the feature vector for sentence 1 ('The cat sat on the hat')?

    <p>{ 2, 1, 1, 1, 1, 0, 0, 0 } (D)</p> Signup and view all the answers

    Why is it necessary to choose a maximum vocabulary size when using the Bag of Words model with a large dataset?

    <p>To limit the length of feature vectors and control the dimensionality. (B)</p> Signup and view all the answers

    What does the CountVectorizer do?

    <p>It automatically performs preprocessing, tokenization, and stop word removal. It then translates the text into a numeric representation (matrix.) (A)</p> Signup and view all the answers

    If the vocabulary is {the, quick, brown, fox, jumps}, and the sentence is 'the quick fox jumps over the lazy dog', what will be the correct feature vector?

    <p>{ 2, 1, 0, 1, 1} (B)</p> Signup and view all the answers

    What would be a plausible feature vector if there are 8 words total in the vocabulary, and only one appears 3 times in a document, another word appears twice, and the rest appear once or not at all?

    <p>{3, 2, 1, 0, 0, 0, 1, 0} (D)</p> Signup and view all the answers

    Which of these is NOT a typical step for preparing text for a Bag of Words model?

    <p>Splitting the text into sentences. (B)</p> Signup and view all the answers

    What happens after the training reviews are cleaned?

    <p>They are converted into numerical representations for machine learning. (B)</p> Signup and view all the answers

    Flashcards

    Labeled Training Data

    A collection of reviews with a positive or negative sentiment label.

    Test Set

    A set of reviews used to evaluate the performance of a trained sentiment analysis model.

    ID

    A unique identifier assigned to each movie review in the dataset.

    Sentiment Score

    A numerical value representing the sentiment of a movie review, typically 0 for negative and 1 for positive.

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    Review Text

    The text content of a movie review.

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    Text Preprocessing

    The process of removing irrelevant or noisy data from the text, such as HTML tags or punctuation, to prepare it for analysis.

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    Beautiful Soup

    A library used to remove HTML markup from text. It helps clean text by extracting only the actual content.

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    re

    A Python library used for regular expression operations. It helps remove punctuation and numbers from text.

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    Feature Engineering

    The process of converting textual data into numerical features suitable for machine learning algorithms.

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    Bag of Words Model

    A machine learning technique that represents text as a collection of words and their frequencies, ignoring word order.

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    Random Forest

    A type of machine learning classifier that uses an ensemble of decision trees to make predictions.

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    Test Dataset

    A set of reviews used to evaluate the performance of a trained model after it has been trained on the training data.

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    Sentiment Prediction

    The process of using a trained model to predict the sentiment (positive or negative) of unseen reviews.

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    re.sub('[^a-zA-Z]', ' ', review)

    A regular expression (regex) statement that finds and replaces characters that are not lowercase or uppercase letters with a space.

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    Tokenization

    The process of breaking down text into individual words or units.

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    Stop Words

    Words that occur frequently in a language but don't carry much meaning, such as "a", "and", "is", and "the".

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    NLTK (Natural Language Toolkit)

    A Python library offering a collection of tools for natural language processing, including a list of stop words.

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    Removing stop words

    The process of removing stop words from text.

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    Bag of Words

    A technique used to group words and their frequencies into a vector, representing the content of the text.

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    Reusable Function

    A function that can be reused to clean multiple reviews.

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    Vocabulary

    A collection of unique words found in a set of documents. It defines the vocabulary used to represent texts as numerical features.

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    Feature Vector

    A numerical representation of a document, where each element corresponds to the count of a particular word in the document's vocabulary.

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    Maximum Vocabulary Size

    A technique used to reduce the dimensionality of feature vectors by selecting only the most frequently occurring words, thereby creating a more manageable representation of text data.

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    CountVectorizer

    A method for creating features from text data using word frequencies, implemented in the scikit-learn library.

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    Scikit-learn

    A library in Python that offers a wide range of tools for text processing, including tokenization, stop word removal, and stemming.

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    Study Notes

    Introduction to Natural Language Processing - Sentiment Analysis Case Study

    • The case study focuses on sentiment analysis using 50,000 IMDB movie reviews.
    • The dataset includes a training set (25,000 reviews) and a test set (25,000 reviews).
    • Sentiment is binary: IMDB ratings less than 5 = 0 (negative), 5 or greater = 1 (positive).
    • The training data does not include any reviews from the test set.
    • Data fields are unique ID (id), sentiment label (1 for positive, 0 for negative), and review text.

    Reading the Data

    • The labeled TrainData.tsv file contains tab-separated data (id, sentiment, review).
    • Use pandas to read the file into a dataframe.
    • header = 0 specifies the first row contains column names.
    • delimiter = "\t" indicates tab as the column separator.
    • quoting = 3 tells Python to ignore double quotes.

    Reading the Data - Verification

    • train.shape returns the dimensions (rows, columns) of the dataframe, confirming the correct size of the data.
    • train.columns.values shows the column names.
    • train.iloc[0] displays the first row of the dataframe for manual verification.

    Reading the Data - Review Examples

    • The reviews are text-based and can provide insight into the sentiment expressed.
    • A few example reviews are shown, demonstrating the content.

    Data Cleaning and Text Preprocessing

    • Remove HTML tags using BeautifulSoup package.
    • The steps for cleaning the data (removing HTML tags, punctuation marks and digits) can be performed in a sequence.

    Dealing with Punctuation, Numbers and Stopwords:

    • Data cleaning considers punctuation and numbers.
    • Removing punctuation and numbers uses a regular expression.
    • Stopwords, frequently occurring words with little meaning, are identified and removed (e.g., "the","a").
    • Python's nltk library can be used to get a list of English stopwords.

    Dealing with Punctuation, Numbers and Stopwords: (Function)

    • review_to_words() function processes reviews for punctuation removal.
    • Stopwords are converted to a set for optimized searching.
    • The function returns processed reviews.

    Dealing with Punctuation, Numbers and Stopwords: (Loop for processing)

    • clean_train_reviews list is created to hold processed reviews.
    • A loop iterates through the entire training dataset and applies the review_to_words() function to each element in the dataset, preserving it in the clean_train_reviews list.

    Creating Features From A Bag Of Words (Using Scikit-Learn)

    • The Bag-of-Words model counts word occurrences in each document to create numeric features.
    • Vocabulary is generated from training set documents.
    • CountVectorizer creates feature vectors from the cleaned reviews.
    • A maximum vocabulary size (5000 most frequent words) is frequently used to limit the feature vector size.

    Apply ML Algorithm

    • A RandomForestClassifier is initialized with 100 trees.
    • The trained model (forest) is used to predict sentiment on new data.

    Assignment Task

    • Use the trained RandomForest model to predict sentiment on a separate test dataset.
    • Format the output as a dataframe (.csv or .xlsx).
    • Crucial: Do not fit the model to the test data. Only use the trained model from the training set for prediction.

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    Description

    Test your knowledge of sentiment analysis using the Bag of Words model and Random Forest classifiers in the context of IMDB movie reviews. This quiz covers key concepts, model evaluation, and data handling techniques essential for achieving accurate predictions. Perfect for students and enthusiasts of data science and natural language processing.

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