JSON-Stream-Reduce

This is a simplified framework built off Mapbox's tile-reduce to perform map-reduce functions against large files of line-delimited JSON. This simply removes all of the tile processing and instead passes each new line in the file to the map script.

This is currently used for geometry-reconstruction of historical OpenStreetMap objects as output from the OSM-Wayback utility

Install

npm install json-stream-reduce

Example Implementation

File: example/index.js

var count = 0;

streamReduce({
  map: path.join(__dirname, 'map.js'),             //Map function
  file: path.join(__dirname, 'file.jsonseq'),      //Input file (lines of JSON)
  maxWorkers:10 // The number of cpus you'd like to use
})
.on('reduce', function(res) {
  count+=res
})
.on('end', function() {
  console.log("Finished with count value: "+count)
});

File: example/map.js

module.exports = function(line, writeData, done) {
  var object = JSON.parse(line.toString());
  done(object.count)
})

file.jsonseq

{"count":10}
{"count":10}
{"count":10}
{"count":10}
{"count":10}

Use

$ node examples/index.js

>>Starting up 2 workers... Job started.
>>Processing lines from file: examples/file.jsonseq
>>5 lines processed in 0s.
>>Finished, value of count: 50