mongodb map reduce advantage usage.

mapper.js

const mapper = function() {
  const value = {
    country: this.country,
    province: this.province,
    city: this.city,
    region: this.region,
    wifi: this.wifi,
    app_version: this.app_version,
    os_version: this.os_version,
    os: this.os,
    network_type: this.network_type,
    channel: this.channel,
    referrer: this.referrer,
    id: this.distinct_id,
  };
  const key = new Date(this.time);
  key.setDate(key.getDate());
  key.setHours(0);
  key.setMinutes(0);
  key.setSeconds(0);
  key.setMilliseconds(0);
  emit(key, value);
};

const reducer = function(key, values) {
  const initial = { count: 0, unique: 0, avg: 0, ids: {} };
  const f = function(id, { count, by_ids }) {
    by_ids[id] = by_ids.hasOwnProperty(id) ? by_ids[id] + 1 : 1;
    count++;
    return { count, by_ids };
  };

  // 除了ID以外都要归约化
  const initialState = {
    summary: { count: 0, unique: 0, by_ids: {} },
  };

  const _mapper = (obj, key, id) => {
    const data = obj ? obj : { count: 0, unique: 0, by_ids: {} };
    return Object.assign(data, f(id, data));
  };

  const toKey = field => `by_${field}`;

  return values.reduce(function(acc, curr) {
    const { id } = curr;
    const fields = Object.keys(curr).filter(key => key !== "id");

    fields.forEach(field => {
      // 初始化维度值
      // key = by_$field
      const key = toKey(field);
      const value = curr[field];

      // acc[by_$field] = {}
      acc[key] = acc.hasOwnProperty(key) ? acc[key] : {};
      // acc[by_$field][$value] = { {count: 0, unique: 0, by_ids: {}}}
      Object.assign(acc[key], { [value]: _mapper(acc[key][value], value, id) });
    });

    return Object.assign(acc, { summary: f(id, acc.summary) });
  }, initialState);
};

const finalize = function(key, value) {
  const f = ({ count, by_ids }) => {
    var unique = Object.keys(by_ids).length || 0;
    var avg = 0;
    if (count > 0) {
      avg = unique / count;
    }
    return { avg, unique };
  };
  const byf = by => Object.keys(by).map(key => ({}));

  const newValue = Object.keys(value)
    .filter(field => field !== "summary")
    .map(field => {
      const v = Object.keys(value[field])
        .map(key => ({
          [key]: Object.assign(value[field][key], f(value[field][key])),
        }))
        .reduce((acc, curr) => Object.assign(acc, curr));
      return { [field]: v };
    })
    .reduce((acc, curr) => Object.assign(acc, curr), {});

  return Object.assign(newValue, {
    summary: Object.assign(value.summary, f(value.summary)),
  });
};

conn = new Mongo();
db = conn.getDB("spinach");
db.myresults.drop();
db.user_signup.mapReduce(mapper, reducer, {
  out: "myresults",
  finalize,
});