data-encoder.js

const _ = require ('lodash');
const DataMapper = require ('./data-mappers/dataMapper');

class DataEncoder {
  /**
     * @param data {Array} of Objects
     * @param mappingObj {Object}
     * */
  _tranformData (data, mappingObj) {
    const emptyMappingObj = {};
    let _mappingObj = {};
    const transformedData = {};
    let columns = [];
    const result = [];
    const transformedColumns = [];

    //create a empty mapping array
    _.each (data[0], function (value, key) {
      emptyMappingObj[key] = null;
    });
    //the columns not in the mappingObj will not be touched
    _mappingObj = _.defaults (mappingObj, emptyMappingObj);

    //apply the encoder to each column
    _.each (data[0], (value, key) => {
      const mapping = _mappingObj[key];
      if (mapping && mapping instanceof DataMapper) {
        const pickedRow = _.map (data, function (row) {
          return row[key];
        });
        transformedData[key] = mapping[this.transformMethod] (pickedRow, key);
      }
    });

    //concat every value in one single row
    _.each (transformedData, function (featureData, feature) {
      columns = _.concat (columns, featureData.columns);
      transformedColumns.push (feature);
      _.each (featureData.values, function (row, index) {
        if (result[index] === undefined) {
          result[index] = [];
        }
        result[index] = _.concat (result[index], row);
      });
    });

    //append the unmapped columns values to the final result
    const unchangedColumns = _.difference (
      _.keys (_mappingObj),
      transformedColumns
    );
    _.each (data, function (row, index) {
      _.each (unchangedColumns, function (column) {
        result[index] = _.concat (result[index], [data[index][column]]);
      });
    });

    return {columns: _.concat (columns, unchangedColumns), values: result};
  }

  /**
     * @param data {Array} of Objects
     * @param mappingObj {Object}
     * */
  fitTransform (data, mappingObj) {
    this.transformMethod = 'fitTransform';
    return this._tranformData (data, mappingObj);
  }

  /**
     * @param data {Array} of Objects
     * @param mappingObj {Object}
     * */
  transform (data, mappingObj) {
    this.transformMethod = 'transform';
    return this._tranformData (data, mappingObj);
  }
}

module.exports = DataEncoder;