js计算数组中某个元素重复出现的个数

    var alarmvalue = ["2_0.500000_0.800000_1.000000;3_0.500000_0.800000_0.757255;6_0.500000_0.800000_1.000000;8_0.500000_0.800000_0.920000", "2_0.500000_0.800000_1.000000;3_0.500000_0.800000_0.609366","0_0.500000_0.800000_0.573164;2_0.500000_0.800000_1.000000;3_0.500000_0.800000_0.702832;6_0.500000_0.800000_1.000000;8_0.500000_0.800000_1.000000"]

    var nArr = [];
    for (var j = 0; j < alarmvalue.length; j++) {
        var alarmStr = alarmvalue[j].split(";");
        for (var i = 0; i < alarmStr.length; i++) {
            nArr.push(alarmStr[i].split("_")[0])
        }
    }

    function getRepeatNum(arr) {
        return arr.reduce(function (prev, next) {
            prev[next] = (prev[next] + 1) || 1;
            return prev;
        }, {});
    }

 var dataList = getRepeatNum(nArr);
    function getDataList(dataList, num) {
        if (dataList[num] == undefined) {
            return 0;
        } else {
            return dataList[num];
        }
    }