Aggregate Data From Dictionaries | Dataford Interview Questions

Insight Data Science receives event records as a list of dictionaries. Write a function that groups the records by one dictionary field and calculates both the number of records and the sum of a numeric field for each group.

Return one dictionary per group in the order each group first appears in the input. Each result dictionary must contain the grouping field, count, and total.

Formal Specification

Implement aggregate_records(records, group_key, metric_key).

records is a list of dictionaries.
group_key and metric_key are strings naming fields present in every record.
records[i][metric_key] is an integer or floating-point number.
Return a list of dictionaries. Each dictionary has group_key mapped to a group value, count mapped to the number of records in that group, and total mapped to the sum of the metric values.
Preserve first-seen group order. Do not mutate records.

Constraints

0 <= len(records) <= 10^5
Each group value is hashable
Every record contains both requested fields
Metric values are finite integers or floating-point numbers
group_key is not count or total

Function Signature

def aggregate_records(records, group_key, metric_key):

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