Q: How to create a dynamic object with data obtained from subtraction of 2 other objects in Node.JS? I've a use case in which I need to generate the object with present and previous month's(or quarter or week) data and also the difference between them too.
I've got the whole data. But I'm confused on how to perform the subtraction among object values and create a new object with it's results.
For example, I've the following data.
data = {
        "variables": [
            "heat",
            "humidity"
        ],
        "lables": [
            "February",
            "January",
            "December",
            "November",
            "October",
            "September"
        ],
        "values": [
            [
                300,
                40,
                0,
                7000,
                250,
                150
            ],
            [
                400,
                10,
                0,
                8000,
                150,
                50
            ]
        ]
}

Now I want to generate the following object.
result= {
        "variables": [
            "heat",
            "humidity"
        ],
        "lables": [
            "February",
            "January",
            "December",
            "November",
            "October",
            "September"
        ],
        "values": [
            [
                300,
                40,
                0,
                7000,
                250,
                150
            ],
            [
                400,
                10,
                0,
                8000,
                150,
                50
            ]
        ],
        "current":{
             "_id":"February",
             "heat":300,
             "humidity":400
        },
        "previous":{
             "_id":"January",
             "heat":40,
             "humidity":10
        },
        "difference":{
             "heat":260,
             "humidity":390
        },
}

Here, the lables and variables are completely dynamic. i.e, if there is only one variable is available, there will be only one array values array. Is there any way to achieve the above result? 

A: You can try something like this:
data.current = {
    _id: data.lables[0],
    ...(data.variables.reduce((obj, variableName, variableIndex) => {
        obj[variableName] = data.values[variableIndex][0]
        return obj
    }, {})
} 
data.previous = {
    _id: data.lables[1],
    ...(data.variables.reduce((obj, variableName, variableIndex) => {
        obj[variableName] = data.values[variableIndex][1]
        return obj
    }, {}))
}
data.difference = {
  ...(data.variables.reduce((obj, variableName, variableIndex) => {
        obj[variableName] = data.current[variableName] - data.previous[variableName]
        return obj
    }, {}))      
}

