Guided Notes

Transform: Data Types, Dates & Encodings

Fixing data types, converting text to numbers, parsing dates, and reading files with unusual encodings.

Why data types matter

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pandas assigns each column a dtype: int64, float64, bool, datetime64, or object/string for text. The type decides what operations do.

The projects data was read with dtype=str, so totalamt is text. Adding text joins it together:

df_projects['totalamt'].sum() β†’ '0200000000580000000…' β€” one giant string, not a total.

The population data, read normally, got sensible types: names as text, years as floats. Always check df.dtypes after extracting.

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