WeightedAverage

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Overview

Use the WeightedAverage gem to calculate the weighted average of a numeric field by using another numeric field as the weight. You can also calculate weighted averages separately for groups of records. The output is an aggregated result set. If no grouping fields are selected, the gem returns a single row containing the weighted average. If grouping fields are selected, it returns one row per group with the grouping fields and the calculated weighted average.

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Prerequisites

Add prophecy_basics package version 1.0.11 or higher to your project.

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Parameters

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How it works

The weighted average is calculated as: $$\frac{\sum (value \times weight)}{\sum weight}$$ Each value is multiplied by its corresponding weight. The results are summed, and that sum is divided by the total weight. If you specify grouping fields, the gem performs this calculation independently for each group.

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Output

If you do not select grouping fields, the gem returns a single row and column with the weighted average. If you select grouping fields, the gem returns one row per group with the weighted average. The output includes the selected grouping fields, if any, and the calculated weighted average using the specified output field name.

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Notes

• Both the Value column and the Weight column must be numeric.
• When weights are equal across all records, the result is the same as a standard average.
• Grouping fields are optional and allow per-group calculations.

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Example

You want to calculate the weighted average price of items sold, where each price is weighted by total_sale value. Input: Configuration:

• Value Field: Price
• Weight Field: Total_Sale
• Output Field Name: weighted_avg_price
• Grouping Fields: (none)

Calculation:

• (20 × 2 + 50 × 1 + 100 × 3) / (2 + 1 + 3)
• (40 + 50 + 300) / 6 = 390 / 6 = 65

Output:

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Example with grouping

If you group by Category: Configuration:

• Grouping Fields: Category

Output: