test.js

gistfile1.txt

const data = [
    {
        roomId: 1,
        rateId: 2,
        name: 'room 1'
    },
    {
        roomId: 1,
        rateId: 2,
        name: 'room 2'
    },
    {
        roomId: 1,
        rateId: 3,
        name: 'room 3'
    },
    {
        roomId: 1,
        rateId: 4,
        name: 'room 4'
    },
]

const grouped = _(data).groupBy((item)=>`${item.roomId}--${item.rateId}`)
const aggregated = grouped.mapValues( v => _.assign(...v))

console.log(JSON.stringify(grouped, null, 2))
console.log(JSON.stringify(aggregated, null, 2))