var groupBy = require('./groupBy')

var objectEach = require('../object/objectEach')

/**
  * 集合分组统计,返回各组中对象的数量统计
  *
  * @param {Array} obj 对象
  * @param {Function} iterate 回调/对象属性
  * @param {Object} context 上下文
  * @return {Object}
  */
function countBy (obj, iterate, context) {
  var result = groupBy(obj, iterate, context || this)
  objectEach(result, function (item, key) {
    result[key] = item.length
  })
  return result
}

module.exports = countBy