How can you eliminate the first elements of two or more arrays of objects until all of their first elements match based on a specific field?

Question

How can you eliminate the first elements of two or more arrays of objects until all of their first elements match based on a specific field?

My Typescript code includes a Map object called `stat_map` defined as

const stat_map: Map<string, IMonthlyStat[]> = new Map();

The interface IMonthlyStat is structured as shown below (Note that there are more fields in reality)

export interface IMonthlyStat {
  month: string;
  value: number;
}

The issue arises when the values within the Map, specifically the IMonthlyStat arrays, contain different month values due to data added at various times.

The format of the month field is '2021-02-01T00:00:00.000 UTC'.

I am looking for the most efficient way to standardize all IMonthlyStat arrays by removing initial elements so they all start with the same month string.

For example, if we have two IMonthlyStat arrays like

[
    {month: '2021-02-01T00:00:00.000 UTC', value: 6}, 
    {month: '2021-03-01T00:00:00.000 UTC', value: 8}, 
    {month: '2021-04-01T00:00:00.000 UTC', value: 10}
]

and

[
    {month: '2021-03-01T00:00:00.000 UTC', value: 7}, 
    {month: '2021-04-01T00:00:00.000 UTC', value: 9}
]

How can I achieve results like this:

[
    {month: '2021-03-01T00:00:00.000 UTC', value: 8}, 
    {month: '2021-04-01T00:00:00.000 UTC', value: 10}
]

and

[
     {month: '2021-03-01T00:00:00.000 UTC', value: 7}, 
     {month: '2021-04-01T00:00:00.000 UTC', value: 9}
]

javascript typescript algorithm

Answer 1

Answer №1

In case you're interested, I have a function below that adjusts an array of arrays so that all arrays begin with the same element, assuming there is at least one common element among them. The comparison of elements is based on a specified key function:

key(A) == key(B) -> A equals B

function alignBy(arrays, keyFunction) {
    for (let item of arrays[0]) {
        let indexes = arrays.map(array => 
            array.findIndex(element => keyFunction(item) === keyFunction(element)))
        if (indexes.every(i => i >= 0))
            return arrays.map((array, index) => array.slice(indexes[index]))
    }
}

//

arrayA = [
    {month: '1', value: 6},
    {month: '2', value: 8},
    {month: '3', value: 10},
    {month: '5', value: 9},
]

arrayB = [
    {month: '2', value: 7},
    {month: '3', value: 9},
    {month: '4', value: 9},
    {month: '6', value: 9},
]

arrayC = [
    {month: '3', value: 7},
    {month: '3', value: 9},
    {month: '4', value: 9},
    {month: '5', value: 9},
]


result = alignBy([arrayA, arrayB, arrayC], x => x.month)
for (item of result) {console.log(...item); console.log('----')}

Answer 2

In case you're interested, I have a function below that adjusts an array of arrays so that all arrays begin with the same element, assuming there is at least one common element among them. The comparison of elements is based on a specified key function:

key(A) == key(B) -> A equals B

function alignBy(arrays, keyFunction) {
    for (let item of arrays[0]) {
        let indexes = arrays.map(array => 
            array.findIndex(element => keyFunction(item) === keyFunction(element)))
        if (indexes.every(i => i >= 0))
            return arrays.map((array, index) => array.slice(indexes[index]))
    }
}

//

arrayA = [
    {month: '1', value: 6},
    {month: '2', value: 8},
    {month: '3', value: 10},
    {month: '5', value: 9},
]

arrayB = [
    {month: '2', value: 7},
    {month: '3', value: 9},
    {month: '4', value: 9},
    {month: '6', value: 9},
]

arrayC = [
    {month: '3', value: 7},
    {month: '3', value: 9},
    {month: '4', value: 9},
    {month: '5', value: 9},
]


result = alignBy([arrayA, arrayB, arrayC], x => x.month)
for (item of result) {console.log(...item); console.log('----')}

Answer 3

Answer №2

const MonthlyData1= [
    {month: '2021-02-01T00:00:00.000 UTC', value: 6}, 
    {month: '2021-03-01T00:00:00.000 UTC', value: 8}, 
    {month: '2021-04-01T00:00:00.000 UTC', value: 10}
]
 
const MonthlyData2= [
    {month: '2021-03-01T00:00:00.000 UTC', value: 7}, 
    {month: '2021-04-01T00:00:00.000 UTC', value: 9}
]

function compareAndRemoveDates(data1, data2){

if (data1 === data2){
    return {
        finalData1: data1,
        finalData2: data2
    }
}
 
const initialDateArray1 = data1[0].month.split('T')[0].split('-')
const initialDateArray2 = data2[0].month.split('T')[0].split('-')

const utcDate1 = new Date(initialDateArray1[0], initialDateArray1[1], initialDateArray1[2]);
const utcDate2 = new Date(initialDateArray2[0], initialDateArray2[1], initialDateArray2[2]);

const dateDiff = utcDate1 < utcDate2 // If true we need to remove Dates in array1 else we need to remove Dates in array2

if(dateDiff){
    return removeDates(data1, data2)
} else {
    return removeDates(data2, data1)
}
}


function removeDates(mutableArr, inmutableArr){
    const initialMonthInmutableArr = inmutableArr[0].month

    while(mutableArr[0].month !== initialMonthInmutableArr){
        mutableArr.shift()
    }

    return {
        finalData1: mutableArr,
        finalData2: inmutableArr
    }    
}

const { finalData1, finalData2 } = compareAndRemoveDates(MonthlyData1, MonthlyData2)

console.log(finalData1)

console.log(finalData2)

/*
[
  { month: '2021-03-01T00:00:00.000 UTC', value: 8 },
  { month: '2021-04-01T00:00:00.000 UTC', value: 10 }
]
[
  { month: '2021-03-01T00:00:00.000 UTC', value: 7 },
  { month: '2021-04-01T00:00:00.000 UTC', value: 9 }
]
*/

Answer 4

const MonthlyData1= [
    {month: '2021-02-01T00:00:00.000 UTC', value: 6}, 
    {month: '2021-03-01T00:00:00.000 UTC', value: 8}, 
    {month: '2021-04-01T00:00:00.000 UTC', value: 10}
]
 
const MonthlyData2= [
    {month: '2021-03-01T00:00:00.000 UTC', value: 7}, 
    {month: '2021-04-01T00:00:00.000 UTC', value: 9}
]

function compareAndRemoveDates(data1, data2){

if (data1 === data2){
    return {
        finalData1: data1,
        finalData2: data2
    }
}
 
const initialDateArray1 = data1[0].month.split('T')[0].split('-')
const initialDateArray2 = data2[0].month.split('T')[0].split('-')

const utcDate1 = new Date(initialDateArray1[0], initialDateArray1[1], initialDateArray1[2]);
const utcDate2 = new Date(initialDateArray2[0], initialDateArray2[1], initialDateArray2[2]);

const dateDiff = utcDate1 < utcDate2 // If true we need to remove Dates in array1 else we need to remove Dates in array2

if(dateDiff){
    return removeDates(data1, data2)
} else {
    return removeDates(data2, data1)
}
}


function removeDates(mutableArr, inmutableArr){
    const initialMonthInmutableArr = inmutableArr[0].month

    while(mutableArr[0].month !== initialMonthInmutableArr){
        mutableArr.shift()
    }

    return {
        finalData1: mutableArr,
        finalData2: inmutableArr
    }    
}

const { finalData1, finalData2 } = compareAndRemoveDates(MonthlyData1, MonthlyData2)

console.log(finalData1)

console.log(finalData2)

/*
[
  { month: '2021-03-01T00:00:00.000 UTC', value: 8 },
  { month: '2021-04-01T00:00:00.000 UTC', value: 10 }
]
[
  { month: '2021-03-01T00:00:00.000 UTC', value: 7 },
  { month: '2021-04-01T00:00:00.000 UTC', value: 9 }
]
*/

Answer 5

Answer №3

Method 1 using array.filter() and array.some()

If I understand correctly, you want to find the common elements between two arrays based on dates.

You can achieve this by using array.filter() and array.some().

Array.filter() will only return elements that meet a specific condition: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter.
Array.some() checks if a certain condition is met within an array and returns the first match: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/some.

You can combine these functions to find elements in array1 where the .month value also exists in array2. For your case, you can repeat this process for both arrays.

The main difference from your original request is that it searches the entire array instead of just looking for the first match, so processing time may be impacted by the array size.

let intersection = array1.filter(x => array2.some(y=> x.month === y.month));

Try running this snippet for a simple demo:

let array1 = [
    {month: '2021-02-01T00:00:00.000 UTC', value: 6},
    {month: '2021-03-01T00:00:00.000 UTC', value: 8},
    {month: '2021-04-01T00:00:00.000 UTC', value: 10}
];

let array2 = [
    {month: '2021-03-01T00:00:00.000 UTC', value: 7},
    {month: '2021-04-01T00:00:00.000 UTC', value: 9}
];

let intersection = array1.filter(x => array2.some(y=> x.month === y.month));
let intersection2 = array2.filter(x => array1.some(y=> x.month === y.month));

console.log(intersection);
console.log(intersection2);

Method 2 with findIndex()

If your arrays are always sorted by month and you're only interested in finding the first matching element, you can follow these steps:

Compare the first items of both arrays to determine the latest month
Use findIndex() to locate the index of that month in each array
Split the arrays based on those indices

Here's a straightforward implementation with slightly more code than the first method but should be more efficient as it only checks the initial item in each array and performs a splice operation:

let array1 = [
    {month: '2021-02-01T00:00:00.000 UTC', value: 6},
    {month: '2021-03-01T00:00:00.000 UTC', value: 8},
    {month: '2021-04-01T00:00:00.000 UTC', value: 10}
];

let array2 = [
    {month: '2021-03-01T00:00:00.000 UTC', value: 7},
    {month: '2021-04-01T00:00:00.000 UTC', value: 9}
];

processedArray1 = [];
processedArray2 = [];

// Find the latest initial month from both arrays
const latestFirstMonth = array1[0].month >= array2[0].month ? array1[0].month : array2[0].month;

// Find the indices of the latest month in each array (since it will be 0 for the array with the latest month initially)
const array1Index = array1.findIndex(element => element.month >= latestFirstMonth);
const array2Index = array2.findIndex(element => element.month >= latestFirstMonth);

// Split the arrays based on these indices
processedArray1 = array1.splice(array1Index);
processedArray2 = array2.splice(array2Index);

console.log(processedArray1);
console.log(processedArray2);

Answer 6

Method 1 using array.filter() and array.some()

If I understand correctly, you want to find the common elements between two arrays based on dates.

You can achieve this by using array.filter() and array.some().

Array.filter() will only return elements that meet a specific condition: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter.
Array.some() checks if a certain condition is met within an array and returns the first match: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/some.

You can combine these functions to find elements in array1 where the .month value also exists in array2. For your case, you can repeat this process for both arrays.

The main difference from your original request is that it searches the entire array instead of just looking for the first match, so processing time may be impacted by the array size.

let intersection = array1.filter(x => array2.some(y=> x.month === y.month));

Try running this snippet for a simple demo:

let array1 = [
    {month: '2021-02-01T00:00:00.000 UTC', value: 6},
    {month: '2021-03-01T00:00:00.000 UTC', value: 8},
    {month: '2021-04-01T00:00:00.000 UTC', value: 10}
];

let array2 = [
    {month: '2021-03-01T00:00:00.000 UTC', value: 7},
    {month: '2021-04-01T00:00:00.000 UTC', value: 9}
];

let intersection = array1.filter(x => array2.some(y=> x.month === y.month));
let intersection2 = array2.filter(x => array1.some(y=> x.month === y.month));

console.log(intersection);
console.log(intersection2);

Method 2 with findIndex()

If your arrays are always sorted by month and you're only interested in finding the first matching element, you can follow these steps:

Compare the first items of both arrays to determine the latest month
Use findIndex() to locate the index of that month in each array
Split the arrays based on those indices

Here's a straightforward implementation with slightly more code than the first method but should be more efficient as it only checks the initial item in each array and performs a splice operation:

let array1 = [
    {month: '2021-02-01T00:00:00.000 UTC', value: 6},
    {month: '2021-03-01T00:00:00.000 UTC', value: 8},
    {month: '2021-04-01T00:00:00.000 UTC', value: 10}
];

let array2 = [
    {month: '2021-03-01T00:00:00.000 UTC', value: 7},
    {month: '2021-04-01T00:00:00.000 UTC', value: 9}
];

processedArray1 = [];
processedArray2 = [];

// Find the latest initial month from both arrays
const latestFirstMonth = array1[0].month >= array2[0].month ? array1[0].month : array2[0].month;

// Find the indices of the latest month in each array (since it will be 0 for the array with the latest month initially)
const array1Index = array1.findIndex(element => element.month >= latestFirstMonth);
const array2Index = array2.findIndex(element => element.month >= latestFirstMonth);

// Split the arrays based on these indices
processedArray1 = array1.splice(array1Index);
processedArray2 = array2.splice(array2Index);

console.log(processedArray1);
console.log(processedArray2);

How can you eliminate the first elements of two or more arrays of objects until all of their first elements match based on a specific field?

Answer №1

Answer №2

Answer №3

Method 1 using array.filter() and array.some()

Method 2 with findIndex()

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