process.js

var cities = ["Albuquerque","Austin","Baltimore","Boston","Charlotte","Chicago","Columbus","Dallas","Denver","Detroit","El Paso","Fairbanks","Fort Worth","Fresno","Houston","Indianapolis","Jacksonville","Kansas City","Las Vegas","Long Beach","Los Angeles","Louisville","Memphis","Mesa","Milwaukee","Nashville","New York","Oklahoma City","Philadelphia","Phoenix","Portland","Sacramento","San Antonio","San Diego","San Francisco","San Jose","Seattle","Tucson","Washington"];

var output = {};

var d3 = require('d3');
var http = require('http');
var fs = require('fs');

cities.forEach(function(city){

  fs.readFile("data/"+city.replace(" ","_")+".json","utf8",function(err,data) {
    var sorted = d3.entries(JSON.parse(data)).map(function(d){

      d.year = parseInt(d.key);

      delete d.key;

      if (!d.value.history.dailysummary[0].meantempi.match(/^-?[0-9]{1,2}$/)) {
        //If it's a weird temperature value, leave it empty
        var temp = "";
      } else {
        var temp = parseInt(d.value.history.dailysummary[0].meantempi);
      }

      d.value = {
        "temp": temp,
        "fall": d.value.history.dailysummary[0].snowfalli.length ? parseFloat(d.value.history.dailysummary[0].snowfalli) : 0,
        "depth": d.value.history.dailysummary[0].snowdepthi.length ? parseFloat(d.value.history.dailysummary[0].snowdepthi) : 0,
        "any": (d.value.history.observations.filter(function(f){
          return f.icon == "snow";
        }).length) ? 1 : 0
      };

      return d;
    }).sort(function(a,b){
      //Sort array by year ascending
      return a.year - b.year;
    });

    output[city] = sorted;

    //Output is full, print it out
    if (d3.keys(output).length == cities.length) console.log(JSON.stringify(d3.entries(output).map(function(d){
      return {
        "city": d.key,
        "data": d.value
      };
    })));
  });

});