JavaScript: organizing data by category with summarization

Question

JavaScript: organizing data by category with summarization

I have a basic JSON list provided below:

{
"myList": [
    {

        "endOfPeriod": 1461362400000,
        "rate": 0.03726378
    },
    {
        "endOfPeriod": 1461535200000,
        "rate": 0.03726378
    },
    {
        "endOfPeriod": 1461967200000,
        "rate": 0.03708314
    },
    {
        "endOfPeriod": 1461708000000,
        "rate": 0.03492851
    },
    {
        "endOfPeriod": 1461794400000,
        "rate": 0.03845068
    },
    {
        "endOfPeriod": 1461621600000,
        "rate": 0.03544827
    }
]

}

In this example, the endOfPeriod value is represented as a Unix epoch timestamp. Although all the timestamps in the sample data correspond to April 2016, they could belong to other time periods as well. Assuming that I have already converted this JSON list into an array and transformed each Unix timestamp into a DD.MM.YYYY date format (or kept them as Unix timestamps), I need to find an effective method to create a new array containing the most recent rate for each month/year group.

The task requires writing JavaScript code.

For instance:

20.04.2016 / 0.33
21.04.2016 / 0.55
14.04.2016 / 0.88
02.05.2016 / 1.33
01.05.2016 / 5.44

The resulting array should include:

21.04.2016 / 0.55
02.05.2016 / 1.33

Thank you for your assistance.

javascript json group-by

Answer 1

Answer №1

If my understanding is correct, you are looking to retrieve the latest rate for each month. My recommendation would be to utilize lodash.

_.chain(data)
  .groupBy(function(entry) {
    var date = new Date(entry.endOfPeriod);
    return date.getFullYear() + '-' + date.getMonth();
  })
  .map(function(group) {
    return _.maxBy(group, function(entry) {
      return entry.endOfPeriod;
    });
  })
  .value()

We begin with a collection of objects structured like this:

{
    "endOfPeriod" : 1464818400000,
    "rate" : 0.05
}

The chain() method encloses the data within a lodash object.

Subsequently, we group the elements by year and month. Following the groupBy() operation, the structure will resemble:

{
  "2016-3" : [array of entries in April 2016],
  "2016-4" : [array of entries in May 2016]
  ...
}

For each group, we identify the item with the highest endOfPeriod.

Lastly, value() reverses the process to transform the lodash object back into a regular Javascript array.

Answer 2

If my understanding is correct, you are looking to retrieve the latest rate for each month. My recommendation would be to utilize lodash.

_.chain(data)
  .groupBy(function(entry) {
    var date = new Date(entry.endOfPeriod);
    return date.getFullYear() + '-' + date.getMonth();
  })
  .map(function(group) {
    return _.maxBy(group, function(entry) {
      return entry.endOfPeriod;
    });
  })
  .value()

We begin with a collection of objects structured like this:

{
    "endOfPeriod" : 1464818400000,
    "rate" : 0.05
}

The chain() method encloses the data within a lodash object.

Subsequently, we group the elements by year and month. Following the groupBy() operation, the structure will resemble:

{
  "2016-3" : [array of entries in April 2016],
  "2016-4" : [array of entries in May 2016]
  ...
}

For each group, we identify the item with the highest endOfPeriod.

Lastly, value() reverses the process to transform the lodash object back into a regular Javascript array.

Answer 3

Answer №2

While I could provide a solution here without relying on lodash, I believe it's best to avoid reinventing the wheel.

const myList = [
  {
    "endOfPeriod": 1461362400000,
    "rate": 0.03726378
  },
  {
    "endOfPeriod": 1461535200000,
    "rate": 0.03726378
  },
  {
    "endOfPeriod": 1461967200000,
    "rate": 0.03708314
  },
  {
    "endOfPeriod": 1461708000000,
    "rate": 0.03492851
  },
  {
    "endOfPeriod": 1461794400000,
    "rate": 0.03845068
  },
  {
    "endOfPeriod": 1461621600000,
    "rate": 0.03544827
  }
];

const res = myList.reduce((prev, current) => {
  const date = new Date(current.endOfPeriod);
  const month = date.getMonth();
  const year = date.getFullYear();

  const key = `${year}-${month}`;

  if (prev[key] && prev[key].endOfPeriod < current.endOfPeriod) {
    prev[key] = current;
  } else {
    prev[key] = current;
  }

    return prev;
}, {});


const finalResult = Object.keys(res).map((key) => {
  return {
    key: res[key].rate
  }
});

console.log(finalResult);

Answer 4

While I could provide a solution here without relying on lodash, I believe it's best to avoid reinventing the wheel.

const myList = [
  {
    "endOfPeriod": 1461362400000,
    "rate": 0.03726378
  },
  {
    "endOfPeriod": 1461535200000,
    "rate": 0.03726378
  },
  {
    "endOfPeriod": 1461967200000,
    "rate": 0.03708314
  },
  {
    "endOfPeriod": 1461708000000,
    "rate": 0.03492851
  },
  {
    "endOfPeriod": 1461794400000,
    "rate": 0.03845068
  },
  {
    "endOfPeriod": 1461621600000,
    "rate": 0.03544827
  }
];

const res = myList.reduce((prev, current) => {
  const date = new Date(current.endOfPeriod);
  const month = date.getMonth();
  const year = date.getFullYear();

  const key = `${year}-${month}`;

  if (prev[key] && prev[key].endOfPeriod < current.endOfPeriod) {
    prev[key] = current;
  } else {
    prev[key] = current;
  }

    return prev;
}, {});


const finalResult = Object.keys(res).map((key) => {
  return {
    key: res[key].rate
  }
});

console.log(finalResult);

JavaScript: organizing data by category with summarization

Answer №1

Answer №2

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