Guided Notes

Transform: Combining Data

Stacking data with concat, joining with merge, and cleaning keys so two sources can match.

Two ways to combine data

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Transforming often starts with bringing sources together:

β€’ concat stacks tables with the same columns on top of each other β€” a union. Rural-population and electricity-access indicators share the same layout (Country Name, Country Code, Indicator Name, year columns), so they stack neatly. β€’ merge joins tables side by side on a shared key β€” like a SQL JOIN. Projects and indicators share a country code and year.

Pick concat when adding rows, merge when adding columns.

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