temp.js

var arr = TheDATA
var tempArr = []
var prev = {
	cityName: ''
}
var result = []
for(var i = 0, len = arr.length;i < len;i ++) {
	
	var currentItem = arr[i]

	if(i === 0) {
		tempArr.push(currentItem)
		prev = currentItem
	}


	else if(i === len - 1 ) {
		var average = computeAve(tempArr)
		result.push({
			cityName: currentItem.cityName
			,price: average
			,date: currentItem.date
		})
	}


	else if(currentItem.cityName !== prev.cityName) {

		var average = computeAve(tempArr)
		result.push({
			cityName: prev.cityName
			,price: average
			,date: currentItem.date
		})
		tempArr = [currentItem]
		prev = currentItem

	}

	else {
		tempArr.push(currentItem)
		prev = currentItem
	}
}