JSFiddle - React, Tailwind, and code Playground

JavaScript

y= [ {"LngTrend":15,"DblValue":10,"DtmStamp":1358226000000},     
{"LngTrend":16,"DblValue":92,"DtmStamp":1358226000000},    
{"LngTrend":17,"DblValue":45,"DtmStamp":1358226000000},
{"LngTrend":18,"DblValue":87,"DtmStamp":1358226000000},


{"LngTrend":15,"DblValue":10,"DtmStamp":1358226060000},
{"LngTrend":16,"DblValue":87,"DtmStamp":1358226060000},
{"LngTrend":17,"DblValue":45,"DtmStamp":1358226060000},
{"LngTrend":18,"DblValue":92,"DtmStamp":1358226060000} ];

var x = {};
var i = y.length;
while(i--) {
    var sHash = y[i].DtmStamp.toString();
    if (typeof(x[sHash]) == "undefined") 
        x[sHash] = [];
    x[sHash].push(y[i].DblValue);
}

alert(JSON.stringify(x));