A z-score rescales and centers a data set around a mean of 0, showing whether each value lies above or below that center. section 2.20
Flag unusually distant trips
Apply scipy.stats.zscore to trip distances, then find every distance whose absolute z-score exceeds 3. This turns an outlier question into a direct filtering task. section 2.20
df = df.dropna().copy()
For a complete-data workflow, create a copy after dropping rows with missing values before continuing analysis. section 2.20
