Practice / strings dates nulls
Waveform wants a clean signup table for reporting — no blank regions.
signups
Your task: return all columns, but replace any null region with the string "unknown". Every row must be kept.
Assign your answer DataFrame to result. Row order doesn't matter.
signupsinput DataFrame| column | type |
|---|---|
| user_id | long |
| region | string |
| user_id | region |
|---|---|
| 1 | EU |
| 2 | null |
| 3 | US |
| 4 | null |
user_idregion· 4 rowsF.coalesce(F.col("region"), F.lit("unknown")) returns the first non-null of
its arguments. Assign it back to region with withColumn, keeping all rows.
This problem builds on Strings, Dates & Nulls (~8 min). Pop it open in a new tab if you want a quick recap.