Convert object of arrays to array of objects

Question

I have source data in the following format (object of arrays):

{
    value: [
      59, 58, 62, 58, 56, 57, 57, 65, 81, 81
    ],
    dayOfWeek: [
      'Thursday', 'Friday', 'Saturday', 'Thursday', 'Friday', 'Friday',
      'Friday',   'Monday', 'Friday',   'Tuesday'
    ],
    dayOrNight: [
      'N', 'D', 'N', 'D', 'D', 'N', 'N', 'N', 'N', 'N'
    ]
}

And I want the data transformed into the following format (array of objects):

[
    {
        value: 59,
        dayOfWeek: 'Thursday',
        dayOrNight: 'N'
    },
    {
        value: 58,
        dayOfWeek: 'Friday',
        dayOrNight: 'D'
    },
    {
        value: 62,
        dayOfWeek: 'Saturday',
        dayOrNight: 'N'
    },
    ...
]

This is kinda the opposite of this question.

What is the appropriate combination of commands to do this, whether using e.g. lodash or otherwise?

StepUp · Accepted Answer · 2020-09-03 20:00:41Z

2

Combining map method and accessing by key to object, we can achieve desired result:

data.value.map((s, i) => ({value: s, 
   dayOfWeek: data.dayOfWeek[i], dayOrNight: data.dayOrNight[i]}));

An example:

let data = {
    value: [
      59, 58, 62, 58, 56, 57, 57, 65, 81, 81
    ],
    dayOfWeek: [
      'Thursday', 'Friday', 'Saturday', 'Thursday', 'Friday', 'Friday',
      'Friday',   'Monday', 'Friday',   'Tuesday'
    ],
    dayOrNight: [
      'N', 'D', 'N', 'D', 'D', 'N', 'N', 'N', 'N', 'N'
    ]
};

const result = data.value.map((s, i) => ({value: s, 
   dayOfWeek: data.dayOfWeek[i], dayOrNight: data.dayOrNight[i]}));
console.log(result);

UPDATE:

This is slightly modified your approach:

let data = {
    value: [
      59, 58, 62, 58, 56, 57, 57, 65, 81, 81
    ],
    dayOfWeek: [
      'Thursday', 'Friday', 'Saturday', 'Thursday', 'Friday', 'Friday',
      'Friday',   'Monday', 'Friday',   'Tuesday'
    ],
    dayOrNight: [
      'N', 'D', 'N', 'D', 'D', 'N', 'N', 'N', 'N', 'N'
    ]
};

const result = Object.values(data)[0].map((s, i) => {
    let obj = {};
    for (let key in data) {
            obj[key] = data[key][i];
    }
    return obj;
});
console.log(result);

edited Sep 3, 2020 at 20:00

answered Sep 3, 2020 at 19:32

StepUp

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6 Comments

drmrbrewer Over a year ago

neat! any way of doing this without having to include the property names? Ideally it would be generic and future-proof to deal with any number of different properties, not just those that happen to be present in the data now. Other than maybe naming the property that is used as the basis for the map function (i.e. value here)... the rest would ideally not be named specifically.

StepUp Over a year ago

@drmrbrewer thanks! what names would you insert instead of dayOrNight, dayOfWeek, value if there would not be property names?

drmrbrewer Over a year ago

sorry, by "not including the property names" I mean not hard-coding them into the conversion function, but just reading them dynamically from the source data object instead. That way, if a new array is added to the data object later (with a new property name) it would automatically be handled by the conversion function still... probably just loop through the keys in the object... I'll give it a try unless you get there first!

StepUp Over a year ago

@drmrbrewer I slightly modified your approach, please, see my updated reply.

drmrbrewer Over a year ago

ah yes, neatly side-stepping the arbitrary use of one of the object properties as a basis for the map function.

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