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Dart vs FxDart › #30 · Three consecutive readings over the limit

Three consecutive readings over the limit

FxDart wins

• zip3
• drop
• filter
• map
• join

Requirement

Hourly CO2 readings for one day. Flag every window of three consecutive readings all above 1000 ppm — that means the ventilation could not catch up for three straight hours — and print each window as a start–end hour range under a header line. The data is in the code below; both versions must print the lines shown under Expected output.

Ventilation alerts (3h over 1000 ppm):
11:00–13:00
15:00–17:00

Side by side

Why they differ

Core Dart has no sliding window, so the native version is an index loop with an i + 2 < length bound and three manual lookups — correct, but every piece of it is bookkeeping a reader must check. The FxDart version builds the window as data: zip3 the list with itself shifted by one and by two (drop(1), drop(2)), and each element becomes a (reading, next, next-next) triple — no indices anywhere. zip3 stopping at the shortest input is exactly the window-fits-entirely rule the loop encodes as its bound. Widening the window to 4 hours is one more shifted input, not a re-audit of the arithmetic.

The shifted inputs are not copies. drop(n) over a List is a range of that list, and zip3 reads all three ranges by index — so the pipeline walks the readings once and allocates one triple per window, which is why its bar sits close to the loop rather than at a multiple of it.