Where the Numbers Settle

A easy Python interview practice problem on DataDriven. Write and execute real python code with instant feedback.

Domain

Python

Difficulty

easy

Seniority

L5

Problem

Sensor readings arrive one at a time, and a dashboard has to show the running mean for each sensor at any moment. Implement a `StreamAverager` class: `add(key, value)` records one numeric reading under `key`, and `get_averages()` returns a dict mapping each key seen so far to the mean of its readings, or an empty dict before anything is recorded. A driver `run_stream_averager(operations)` is provided: `operations` is a list where each entry is either `['add', key, value]` or `['get_averages']`. Build one `StreamAverager`, apply the operations in order, and return a parallel list of results, with `None` for each `'add'` and the dict for each `'get_averages'`. Means are floats, so `add('sensor_a', 10)`, `add('sensor_a', 30)`, `get_averages()` gives `{'sensor_a': 20.0}`.

Summary

The answer moves with the data.

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