relation algebra

gistfile1.js

function Relation(schema, data)
{
  this.schema = schema;
  this.data = data;

  // only supports equals for now
  this.s = function(attribute, value) {
    var index = this.schema.indexOf(attribute);
    var new_data = this.data.filter(function(datum) {
      return datum[index] == value;
    });

    return new Relation(schema, new_data);
  }

  this.p = function(attribute/* , attributeN */) {
    var schema = [];
    var mapping = {};
    for ( var i = 0, _len = arguments.length; i < _len; i++)
    {
      var attribute = arguments[i];
      schema.push(attribute);
      mapping[attribute] = this.schema.indexOf(attribute);
    };

    var new_data = this.data.map(function(datum) {
      var new_datum = [];

      for (attribute in mapping)
      {
        new_datum.push(datum[mapping[attribute]]);
      };

      return new_datum;
    });

    return new Relation(schema, new_data);
  };
};


// db

Student = new Relation(['sID', 'sName', 'GPA', 'sizeHS'],
  [
    [1, 'Rocky', 4.0, 1000]
  , [2, 'Gavin', 3.9, 800]
  , [3, 'Paula', 4.2, 2200]
  ]);

Application = new Relation(['sID', 'cName', 'major', 'dec'],
  [
    [1, 'UCD', 'PSCI', 'A']
  , [1, 'MIT', 'CS', 'A']
  , [2, 'MIT', 'CS', 'R']
  , [3, 'Metro', 'CS', 'A']
  ]);

// tests

console.log(Student.s('sName', 'Rocky'));
console.log(Student.s('sName', 'Rocky').p('sID'));
console.log(Student.p('sID', 'GPA'));