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Time Series with PyTorch
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Dictionary-based approaches are somewhat similar to shapelet algorithms, in that they slide windows over a series to find phase-independent subsequences. The difference comes in that they use patterns that appear within a series like words in text analysis. In text classification we use a Bag-of-Words (BoW) to count word occurrences; similarly, time series dictionaries track frequency of ‘pattern’ occurrence.
The classic approach to this comes from Symbolic Aggregate approXimation (SAX), which discretizes a series’ segments into a symbol/word-based representation. A Bag-of-Patterns (BoP) algorithm extends this by sliding a window across each series, converting windowed segments into symbolic words, then using frequencies to build a histogram of pattern occurrences. This feature representation captures recurring motifs while being invariant to their position within the series.

Figure 14.20: Diagram of dictionary approach...