pluckTest.js

// Setup
var assignments = [];
var _ = require('underscore');

function pluckUnique(arrayOfObj, key) {
  var pluckedValues = {};
  arrayOfObj.forEach(function(obj) {
    var valAtKey = obj[key];
    if (pluckedValues[valAtKey]) {
      pluckedValues[valAtKey]++;
    } else {
      pluckedValues[valAtKey] = 1;
    }
  });
  return _.keys(pluckedValues);
}

// Different assignments
for (let i = 0; i < 5000; i++) {
  var assignment = {
    id: i,
    assignable_id: 1754593,
    user_id: i,
    starts_at: '2018-03-10',
    ends_at: '2018-04-10',
    all_day_assignment: true,
    allocation_mode: 'percent',
    description: 'A description',
    status: null,
    fixed_hours: null,
    repetition_id: null,
    resource_request_id: null,
  }
  assignments.push(assignment);
}

// 5000 duplicate assignments
for (let i = 0; i < 5000; i++) {
  var assignment = {
    id: 5000,
    assignable_id: 1754593,
    user_id: i,
    starts_at: '2018-03-10',
    ends_at: '2018-04-10',
    all_day_assignment: true,
    allocation_mode: 'percent',
    description: 'A description',
    status: null,
    fixed_hours: null,
    repetition_id: null,
    resource_request_id: null,
  }
  assignments.push(assignment);
}

console.log('Testing lodash implementation');

console.time('lodash');
var ids = _.uniq(_.pluck(assignments, 'id'));
console.timeEnd('lodash');


console.log('Testing optimized version');
console.time('optimized');
var ids2 = pluckUnique(assignments, 'id');
console.timeEnd('optimized');