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👀 What is Seasonality?

一個固定的圖形樣式(pattern)，以每一個固定頻率循環一次，這個樣式就稱做一個Seasonality

其中一個例子是某個店家的每年銷貨總額，會以每一個年出現一個相同的樣式 另一個例子是電力需求量，會以每天為一個單位，出現一個同樣的樣式(當然，這樣一來每周、每個月、每年也可以是一個單位)

💭 What is Cyclical Patterns?

雖然圖形有某種特定樣式，但不會在固定某個週期循環一次，這個樣式稱做Cyclical Patterns

例如加拿大的山貓數量、美國每個月房地產成交的件數

🛫 那麼要得到Seasonality和Cyclical Features要取那些特徵?

Seasonality

• Lag Features
• Calendar Features — datetime features
• Seasonal Dummies —- seasonal indicators
• Fouries Features —- infinite series of sine and cosine functions

Cyclical Features

• Lag Features