fbjs/lib/countDistinct.js.flow

A collection of utility libraries used by other Facebook JS projects

/**
 * Copyright (c) 2013-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @providesModule countDistinct
 * @flow
 */
'use strict';

var emptyFunction = require("./emptyFunction");
/**
 * Returns the count of distinct elements selected from an array.
 */


function countDistinct<T1, T2>(iter: Iterable<T1>, selector: (item: T1) => T2): number {
  selector = selector || emptyFunction.thatReturnsArgument;
  var set = new Set();

  for (var val of iter) {
    set.add(selector(val));
  }

  return set.size;
}

module.exports = countDistinct;