turf.propReduce

What is turf.propReduce?

turf.propReduce folds every Feature's properties object into a single accumulator. It is the attribute-only counterpart to featureReduce.

turf.propReduce(geojson, callback, initialValue?) → any

The callback receives (previousValue, currentProperties, featureIndex).

When would you use turf.propReduce?

Use turf.propReduce to build summaries that depend only on attributes — totalling a population property, collecting unique values of a category, or constructing an id-to-name lookup. Because geometry is ignored it is slightly faster and signals intent.

1const totalPopulation = turf.propReduce(
2  tracts,
3  (sum, props) => sum + (props.population ?? 0),
4  0
5);

FAQs

How do I install Turf.js to use this function?

Install npm install @turf/meta and import with import { propReduce } from '@turf/meta', or use the umbrella @turf/turf bundle.

What if a Feature has null or missing properties?

The callback receives null for those. Use optional chaining (props?.key) or a fallback inside your reducer to stay safe.

Can I mutate the accumulator?

Yes — mutating a Map or array inside the reducer is fine for performance. Return the accumulator at the end of every iteration.

Should I use propReduce or loop the features array directly?

Both work. propReduce handles single-Feature and bare-Geometry inputs seamlessly, whereas looping requires guarding against those shapes. Use the Turf helper for robustness.