NO.PZ2021083101000014
问题如下：
As an additional part of the text exploration step, Achler conducts a term frequency analysis to identify outliers. Achler summarizes the analysis in Exhibit 2.
Based on Exhibit 2, Achler should exclude from further analysis words in:
选项：
A.
only Group 1
B.
only Group 2
C.
both Group 1 and Group 2
解释：
C is correct.
Achler should remove words that are in both Group 1 and Group 2. Term frequency values range between 0 and 1. Group 1 consists of the highest frequency values (e.g., “the” = 0.04935), and Group 2 consists of the lowest frequency values (e.g., “naval” = 1.0123e–05).
Frequency analysis on the processed text data helps in filtering unnecessary tokens (or features) by quantifying how important tokens are in a sentence and in the corpus as a whole.
The most frequent tokens (Group 1) strain the machine-learning model to choose a decision boundary among the texts as the terms are present across all the texts, which leads to model underfitting.
The least frequent tokens (Group 2) mislead the machine-learning model into classifying texts containing the rare terms into a specific class, which leads to model overfitting. Identifying and removing noise features is critical for text classification applications.
A is incorrect because words in both Group 1 and Group 2 should be removed.
The words with high term frequency value are mostly stop words, present in most sentences. Stop words do not carry a semantic meaning for the purpose of text analyses and ML training, so they do not contribute to differentiating sentiment.
B is incorrect because words in both Group 1 and Group 2 should be removed.
Terms with low term frequency value are mostly rare terms, ones appearing only once or twice in the data. They do not contribute to differentiating sentiment.
考点：Unstructured Data Exploration
frequency不是0—1吗？！Group 1这些词的频率是0.0几，不算高吧？
