Interview Q&A / Data Science

1. What is the difference between normalisation and standardisation?

   Normalisation (min-max scaling) squeezes values into a fixed range, usually 0 to 1, using (x - min) / (max - min). Standardisation (z-score scaling) shifts values to mean 0 and standard deviation 1, using (x - mean) / std. Standardisation handles outliers better, and both should be fitted on training data only.

   BeginnerIn-depth4 min read
2. How do you handle missing values in a dataset?

   First find how much is missing and why. Then either drop rows or columns (when little is missing or a column is mostly empty) or fill the gaps, using the median for skewed numbers, the mode for categories, forward fill for time series, or a model-based method. Often add a flag column that records which values were missing.

   IntermediateIn-depth4 min read