LDA が単語をトピックにまとめる仕組み

LDA assumes every document was written by mixing a few topics, and every topic prefers certain words. It works backwards to recover both.

LDA learns two things at once: which topics each document uses, and which words each topic favors. Both are hidden until the model finds them. 🍳

Inside LDA, a topic is a probability over words. A sports topic gives high weight to goal and match, low weight to recipe.

Each document also gets its own mixture: maybe 60% topic one and 40% topic two. That blend explains its word choices.

LDA imagines writing each word by first picking a topic, then drawing a word from it. This generative story is the heart of the model. ✍️

You only see the finished words. LDA infers the hidden topics that most likely produced them, reversing the generative process.

Words that keep co-occurring get pulled into the same topic. Co-occurrence is the main signal LDA uses to group them.

LDA does not guess how many topics exist. You set num_topics up front, and the model fills them in.

LDA uses a bag-of-words view: only which words appear and how often, not their order. Grammar is ignored for theme discovery.

A word can belong to several topics with different weights. LDA gives soft assignments, never forcing a word into just one group.

Latent means hidden, Dirichlet is the math for the mixtures, and Allocation is assigning words. Together they form LDA.

Think about how LDA represents a single document.

LDA assumes topics are word distributions and documents are topic mixtures. It works backwards from co-occurring words to uncover both hidden structures. 🧩