Average Spend Per Customer | Dataford Interview Questions

Whats the average spend per customer (including customers too who haven't purchased anything)?

Asked in the phone interview stage. Implement the calculation without SQL.

Input and Output

Implement average_spend(customers, purchases). customers is a non-empty list of unique customer IDs. purchases is a list of [customer_id, amount] pairs. Return the total amount from purchases belonging to known customers divided by the number of customers. Customers without purchases contribute zero. Ignore purchases for unknown customer IDs.

Constraints

1 <= len(customers) <= 1000
0 <= len(purchases) <= 10000
Customer IDs are unique and hashable
Each purchase is a two-element pair of customer ID and non-negative amount
Purchase amounts are numeric

Function Signature

def average_spend(customers, purchases):

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