Adding ranks to objects in an array
Forgive me if I misunderstand it, but in the second loop isn't the report and reports[report.rank] refer the same object?

Because if so, then the following simpler code would produce the same result:

function (reports) {
    reports.forEach(function (report, i) {
        report.upPercentage = reports.upTime / reports.totalTime;
    });
    _.sortBy(reports, 'upPercentage').forEach(function (report, i) {
        report.rank = i;
    });
    return reports;
}