evenOdd.js

var fs        = require('fs');
var stream    = require('stream');
var byLine    = new stream.Transform({objectMode: true});

var inputFile = fs.createReadStream('uspop.csv',{'encoding': 'utf8'});
var even      = fs.createWriteStream('evenYears.csv');
var odd       = fs.createWriteStream('oddYears.csv');

function evenOddYears (line) {
  // check if year is even or odd
  var currYear = line.slice(0, 4);

  if (parseInt(currYear) % 2 === 0) {
    console.log('even:', currYear);
    even.write(new Buffer(line + '\n'));
  } else {
    console.log('odd:', currYear);
    odd.write(new Buffer(line + '\n'));
  }
}

byLine._transform = function (chunk, encoding, cb) {
  var data = chunk.toString();
  var lines = data.split('\n');
  lines.forEach(evenOddYears);
  cb();
};

inputFile.pipe(byLine).pipe(process.stdout);
process.stdout.on('error', process.exit);

uspop.csv