js计算数组中某个元素重复出现的个数

项目需求

统计数组中每个2_0.500000_0.800000_1.000000中第一"_"前数字的个数，并生成饼图。

    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"]

分离数组

    var nArr = [];
    for (var j = 0; j