minimist = function (args, opts) {
  if (!opts) opts = {};
  var flags = {
    bools: {},
    strings: {},
    unknownFn: null
  };

  if (typeof opts['unknown'] === 'function') {
    flags.unknownFn = opts['unknown'];
  }

  if (typeof opts['boolean'] === 'boolean' && opts['boolean']) {
    flags.allBools = true;
  } else {
    [].concat(opts['boolean']).filter(Boolean).forEach(function (key) {
      flags.bools[key] = true;
    });
  }

  var aliases = {};
  Object.keys(opts.alias || {}).forEach(function (key) {
    aliases[key] = [].concat(opts.alias[key]);
    aliases[key].forEach(function (x) {
      aliases[x] = [key].concat(aliases[key].filter(function (y) {
        return x !== y;
      }));
    });
  });
  [].concat(opts.string).filter(Boolean).forEach(function (key) {
    flags.strings[key] = true;

    if (aliases[key]) {
      flags.strings[aliases[key]] = true;
    }
  });
  var defaults = opts['default'] || {};
  var argv = {
    _: []
  };
  Object.keys(flags.bools).forEach(function (key) {
    setArg(key, defaults[key] === undefined ? false : defaults[key]);
  });
  var notFlags = [];

  if (args.indexOf('--') !== -1) {
    notFlags = args.slice(args.indexOf('--') + 1);
    args = args.slice(0, args.indexOf('--'));
  }

  function argDefined(key, arg) {
    return flags.allBools && /^--[^=]+$/.test(arg) || flags.strings[key] || flags.bools[key] || aliases[key];
  }

  function setArg(key, val, arg) {
    if (arg && flags.unknownFn && !argDefined(key, arg)) {
      if (flags.unknownFn(arg) === false) return;
    }

    var value = !flags.strings[key] && isNumber(val) ? Number(val) : val;
    setKey(argv, key.split('.'), value);
    (aliases[key] || []).forEach(function (x) {
      setKey(argv, x.split('.'), value);
    });
  }

  function setKey(obj, keys, value) {
    var o = obj;

    for (var i = 0; i < keys.length - 1; i++) {
      var key = keys[i];
      if (key === '__proto__') return;
      if (o[key] === undefined) o[key] = {};
      if (o[key] === Object.prototype || o[key] === Number.prototype || o[key] === String.prototype) o[key] = {};
      if (o[key] === Array.prototype) o[key] = [];
      o = o[key];
    }

    var key = keys[keys.length - 1];
    if (key === '__proto__') return;
    if (o === Object.prototype || o === Number.prototype || o === String.prototype) o = {};
    if (o === Array.prototype) o = [];

    if (o[key] === undefined || flags.bools[key] || typeof o[key] === 'boolean') {
      o[key] = value;
    } else if (Array.isArray(o[key])) {
      o[key].push(value);
    } else {
      o[key] = [o[key], value];
    }
  }

  function aliasIsBoolean(key) {
    return aliases[key].some(function (x) {
      return flags.bools[x];
    });
  }

  for (var i = 0; i < args.length; i++) {
    var arg = args[i];

    if (/^--.+=/.test(arg)) {
      // Using [\s\S] instead of . because js doesn't support the
      // 'dotall' regex modifier. See:
      // http://stackoverflow.com/a/1068308/13216
      var m = arg.match(/^--([^=]+)=([\s\S]*)$/);
      var key = m[1];
      var value = m[2];

      if (flags.bools[key]) {
        value = value !== 'false';
      }

      setArg(key, value, arg);
    } else if (/^--no-.+/.test(arg)) {
      var key = arg.match(/^--no-(.+)/)[1];
      setArg(key, false, arg);
    } else if (/^--.+/.test(arg)) {
      var key = arg.match(/^--(.+)/)[1];
      var next = args[i + 1];

      if (next !== undefined && !/^-/.test(next) && !flags.bools[key] && !flags.allBools && (aliases[key] ? !aliasIsBoolean(key) : true)) {
        setArg(key, next, arg);
        i++;
      } else if (/^(true|false)$/.test(next)) {
        setArg(key, next === 'true', arg);
        i++;
      } else {
        setArg(key, flags.strings[key] ? '' : true, arg);
      }
    } else if (/^-[^-]+/.test(arg)) {
      var letters = arg.slice(1, -1).split('');
      var broken = false;

      for (var j = 0; j < letters.length; j++) {
        var next = arg.slice(j + 2);

        if (next === '-') {
          setArg(letters[j], next, arg);
          continue;
        }

        if (/[A-Za-z]/.test(letters[j]) && /=/.test(next)) {
          setArg(letters[j], next.split('=')[1], arg);
          broken = true;
          break;
        }

        if (/[A-Za-z]/.test(letters[j]) && /-?\d+(\.\d*)?(e-?\d+)?$/.test(next)) {
          setArg(letters[j], next, arg);
          broken = true;
          break;
        }

        if (letters[j + 1] && letters[j + 1].match(/\W/)) {
          setArg(letters[j], arg.slice(j + 2), arg);
          broken = true;
          break;
        } else {
          setArg(letters[j], flags.strings[letters[j]] ? '' : true, arg);
        }
      }

      var key = arg.slice(-1)[0];

      if (!broken && key !== '-') {
        if (args[i + 1] && !/^(-|--)[^-]/.test(args[i + 1]) && !flags.bools[key] && (aliases[key] ? !aliasIsBoolean(key) : true)) {
          setArg(key, args[i + 1], arg);
          i++;
        } else if (args[i + 1] && /^(true|false)$/.test(args[i + 1])) {
          setArg(key, args[i + 1] === 'true', arg);
          i++;
        } else {
          setArg(key, flags.strings[key] ? '' : true, arg);
        }
      }
    } else {
      if (!flags.unknownFn || flags.unknownFn(arg) !== false) {
        argv._.push(flags.strings['_'] || !isNumber(arg) ? arg : Number(arg));
      }

      if (opts.stopEarly) {
        argv._.push.apply(argv._, args.slice(i + 1));

        break;
      }
    }
  }

  Object.keys(defaults).forEach(function (key) {
    if (!hasKey(argv, key.split('.'))) {
      setKey(argv, key.split('.'), defaults[key]);
      (aliases[key] || []).forEach(function (x) {
        setKey(argv, x.split('.'), defaults[key]);
      });
    }
  });

  if (opts['--']) {
    argv['--'] = new Array();
    notFlags.forEach(function (key) {
      argv['--'].push(key);
    });
  } else {
    notFlags.forEach(function (key) {
      argv._.push(key);
    });
  }

  return argv;
}
Creates an object composed of keys generated from the results of running
each element of `collection` thru `iteratee`. The order of grouped values
is determined by the order they occur in `collection`. The corresponding
value of each key is an array of elements responsible for generating the
key. The iteratee is invoked with one argument: (value).

@static
@memberOf _
@since 0.1.0
@category Collection
@param {Array|Object} collection The collection to iterate over.
@param {Function} [iteratee=_.identity] The iteratee to transform keys.
@returns {Object} Returns the composed aggregate object.
@example

_.groupBy([6.1, 4.2, 6.3], Math.floor);
// => { '4': [4.2], '6': [6.1, 6.3] }

// The `_.property` iteratee shorthand.
_.groupBy(['one', 'two', 'three'], 'length');
// => { '3': ['one', 'two'], '5': ['three'] }