Problem 3 of 4 · Joins & mergesNext: Apply a batch of changes to an SCD2 dimension

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Practice / Python / Joins & merges

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HardAbout 16 minJoins & merges

As-of join: price effective at each trade

Attach to each trade the most recent price at or before its timestamp, matched per symbol. trades has trade_id, symbol, ts (ISO); prices has symbol, ts, price. A trade with no earlier price for its symbol gets None.

Return the per-trade price (or None), ordered by trade_id.

What the tests check

2 on Run · 3 on Submit

01most recent price at/before trade, per symbol; None if none earlier

02a price stamped exactly at the trade time counts as 'at or before'

Submit runs these and one more check you don’t see, so code written for the visible tests alone can still miss.

Runtime

Python 3.13 in your browser – the standard library plus pandas and numpy; no pip installs.

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