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95 lines
2.2 KiB
Markdown
95 lines
2.2 KiB
Markdown
# Outlier Analysis Worker
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Processes outlier detection jobs to identify statistical outliers in spatial data.
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## Overview
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The outlier analysis worker identifies features with values that are statistically unusual using z-score or MAD (Median Absolute Deviation) methods.
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## Job Type
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`outlier_analysis`
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## Input Parameters
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```json
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{
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"dataset_id": 123,
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"value_field": "income",
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"method": "zscore",
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"threshold": 2.0
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}
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```
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### Parameters
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- `dataset_id` (required): Source dataset ID
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- `value_field` (required): Numeric field to analyze
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- `method` (optional): "zscore" or "mad" (default: "zscore")
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- `threshold` (optional): Z-score threshold or MAD multiplier (default: 2.0)
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## Output
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Creates a new dataset with outlier analysis results:
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- Original features marked as outliers
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- Outlier score (z-score or MAD score)
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- Outlier flag
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- Original attributes preserved
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## Methods
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### Z-Score Method
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Calculates standardized z-scores:
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- Mean and standard deviation calculated
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- Z-score = (value - mean) / standard_deviation
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- Features with |z-score| > threshold are outliers
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### MAD Method
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Uses Median Absolute Deviation:
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- Median calculated
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- MAD = median(|value - median|)
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- Modified z-score = 0.6745 * (value - median) / MAD
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- Features with |modified z-score| > threshold are outliers
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## Example
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```bash
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# Enqueue an outlier analysis job via API
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curl -X POST "https://example.com/api/analysis/outlier_run.php" \
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-H "Content-Type: application/json" \
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-d '{
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"dataset_id": 123,
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"value_field": "income",
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"method": "zscore",
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"threshold": 2.0
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}'
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```
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## Background Jobs
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This analysis runs as a background job. The worker:
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1. Fetches queued `outlier_analysis` jobs
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2. Validates input parameters
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3. Calculates statistics (mean/std or median/MAD)
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4. Identifies outliers
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5. Creates output dataset
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6. Marks job as completed
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## Performance Considerations
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- Processing time depends on dataset size
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- Z-score method requires two passes (mean/std, then scoring)
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- MAD method is more robust to outliers in calculation
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- Consider filtering null values before analysis
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## Related Documentation
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- [Outlier Analysis Tool](../analysis-tools/outliers.md)
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- [Analysis API](../api/analysis.md)
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- [Workers Overview](index.md)
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