Modify an array by incorporating values from another array that have a matching property

Question

Modify an array by incorporating values from another array that have a matching property

I have two arrays that look like this

 let array1 =   [{
      'id': 1,
      'name': 'A'
    }, {
      'id': 2,
      'name': 'B'
    }, {
      'id': 3,
      'name': 'C'
    }]

let array2 =   [{
      'id': 1,
      'name': 'x'
    }, {
      'id': 2,
      'name': 'y'
    }]

My goal is to update the values in array 1 with the corresponding object values from array 2, based on matching id values. The expected result should be:

 [{
      'id': 1,
      'name': 'x'
    }, {
      'id': 2,
      'name': 'y'
    }, {
      'id': 3,
      'name': 'C'
    }]

I tried the following code but it's not functioning correctly.

    array1.forEach(item1 => {
        const itemFromArr2 = array2.find(item2 => item2.id == item1.id);
        if (itemFromArr2) {
           item1 = itemFromArr2;
        }
     })

If you have any suggestions on how to achieve this, please advise. Thank you.

javascript arrays typescript

Answer 1

Answer №1

Take a look at this concise one-liner:

array1.map(e => (e.name = array2.find(a => a.id == e.id)?.name || e.name, e));

Explanation: The code is mapping over array1 and searching for the matching id in array2. If a match is found (

array2.find(a => a.id == e.id)?.name

), it updates the name property to the found value, otherwise it retains the original name.

Here's a small example:

let array1 = [{
  'id': 1,
  'name': 'A'
}, {
  'id': 2,
  'name': 'B'
}, {
  'id': 3,
  'name': 'C'
}]

let array2 = [{
  'id': 1,
  'name': 'x'
}, {
  'id': 2,
  'name': 'y'
}]

const newarray = array1.map(e => (e.name = array2.find(a => a.id == e.id)?.name || e.name, e));
console.log(newarray);

Edit based on @Roster's suggestion, if you want to update the entire entry use this line:

array1.map(e => (e = array2.find(a => a.id == e.id) || e, e));

For another example:

let array1 = [{
  'id': 1,
  'name': 'A'
}, {
  'id': 2,
  'name': 'B'
}, {
  'id': 3,
  'name': 'C'
}]

let array2 = [{
  'id': 1,
  'name': 'x'
}, {
  'id': 2,
  'name': 'y',
  'otherproperty': 42
}]

const newarray = array1.map(e => (e = array2.find(a => a.id == e.id) || e, e));
console.log(newarray);

Answer 2

Take a look at this concise one-liner:

array1.map(e => (e.name = array2.find(a => a.id == e.id)?.name || e.name, e));

Explanation: The code is mapping over array1 and searching for the matching id in array2. If a match is found (

array2.find(a => a.id == e.id)?.name

), it updates the name property to the found value, otherwise it retains the original name.

Here's a small example:

let array1 = [{
  'id': 1,
  'name': 'A'
}, {
  'id': 2,
  'name': 'B'
}, {
  'id': 3,
  'name': 'C'
}]

let array2 = [{
  'id': 1,
  'name': 'x'
}, {
  'id': 2,
  'name': 'y'
}]

const newarray = array1.map(e => (e.name = array2.find(a => a.id == e.id)?.name || e.name, e));
console.log(newarray);

Edit based on @Roster's suggestion, if you want to update the entire entry use this line:

array1.map(e => (e = array2.find(a => a.id == e.id) || e, e));

For another example:

let array1 = [{
  'id': 1,
  'name': 'A'
}, {
  'id': 2,
  'name': 'B'
}, {
  'id': 3,
  'name': 'C'
}]

let array2 = [{
  'id': 1,
  'name': 'x'
}, {
  'id': 2,
  'name': 'y',
  'otherproperty': 42
}]

const newarray = array1.map(e => (e = array2.find(a => a.id == e.id) || e, e));
console.log(newarray);

Answer 3

Answer №2

Transform the update array into a Map, then loop through the target array using Array.map(), and combine it with the object of the corresponding key in the updateMap if it is present:

const mergeArrays = (keySelector, targetArray, updateArray) => {
  const updateMap = new Map(updateArray.map(item => [keySelector(item), item]))
  
  return targetArray.map(item => {
    const key = keySelector(item)
    
    return updateMap.has(key)
      ? { ...item, ...updateMap.get(key)}
      : item
  })
}

const initialArray = [{"id":1,"name":"A"},{"id":2,"name":"B"},{"id":3,"name":"C"}]
const newArray = [{"id":1,"name":"x"},{"id":2,"name":"y"}]

const mergedResult = mergeArrays(o => o.id, initialArray, newArray);
console.log(mergedResult);

With TypeScript support (TS playground):

const mergeArrays = <T>(keySelector: (arg: T) => any, targetArray: T[], updateArray: T[]) => {
  const updateMap = new Map(updateArray.map(item => [keySelector(item), item]))
  
  return targetArray.map(item => {
    const key = keySelector(item)
    
    return updateMap.has(key)
      ? { ...item, ...updateMap.get(key)}
      : item
  })
}

Answer 4

Transform the update array into a Map, then loop through the target array using Array.map(), and combine it with the object of the corresponding key in the updateMap if it is present:

const mergeArrays = (keySelector, targetArray, updateArray) => {
  const updateMap = new Map(updateArray.map(item => [keySelector(item), item]))
  
  return targetArray.map(item => {
    const key = keySelector(item)
    
    return updateMap.has(key)
      ? { ...item, ...updateMap.get(key)}
      : item
  })
}

const initialArray = [{"id":1,"name":"A"},{"id":2,"name":"B"},{"id":3,"name":"C"}]
const newArray = [{"id":1,"name":"x"},{"id":2,"name":"y"}]

const mergedResult = mergeArrays(o => o.id, initialArray, newArray);
console.log(mergedResult);

With TypeScript support (TS playground):

const mergeArrays = <T>(keySelector: (arg: T) => any, targetArray: T[], updateArray: T[]) => {
  const updateMap = new Map(updateArray.map(item => [keySelector(item), item]))
  
  return targetArray.map(item => {
    const key = keySelector(item)
    
    return updateMap.has(key)
      ? { ...item, ...updateMap.get(key)}
      : item
  })
}

Answer 5

Answer №3

Implementing a hashmap to efficiently update an array.

The primary purpose of utilizing a hashmap in this scenario is to enhance performance.

const originalArray = [
    { id: 1, name: "Alpha" },
    { id: 2, name: "Beta" },
    { id: 3, name: "Gamma" },
];

const updatedArray = [
    { id: 1, name: "X" },
    { id: 2, name: "Y" },
];

const hashMap = updatedArray.reduce((accumulator, item) => {
    const { id } = item;
    if (!accumulator[id]) {
        accumulator[id] = item;
    }
    return accumulator;
}, {});

const finalOutput = originalArray.map(item => {
    const newName = hashMap[item.id]?.name;
    if (newName) {
        item.name = newName;
    }
    return item;
});

console.log(finalOutput);

Answer 6

Implementing a hashmap to efficiently update an array.

The primary purpose of utilizing a hashmap in this scenario is to enhance performance.

const originalArray = [
    { id: 1, name: "Alpha" },
    { id: 2, name: "Beta" },
    { id: 3, name: "Gamma" },
];

const updatedArray = [
    { id: 1, name: "X" },
    { id: 2, name: "Y" },
];

const hashMap = updatedArray.reduce((accumulator, item) => {
    const { id } = item;
    if (!accumulator[id]) {
        accumulator[id] = item;
    }
    return accumulator;
}, {});

const finalOutput = originalArray.map(item => {
    const newName = hashMap[item.id]?.name;
    if (newName) {
        item.name = newName;
    }
    return item;
});

console.log(finalOutput);

Answer 7

Answer №4

Below is an approach utilizing Generics:

const array1 =   [{
      'id': 1,
      'name': 'A'
    }, {
      'id': 2,
      'name': 'B'
    }, {
      'id': 3,
      'name': 'C'
    }]

const array2 =   [{
      'id': 1,
      'name': 'x'
    }, {
      'id': 2,
      'name': 'y'
    }]


function mergeArray<T>(arr1: T[], arr2: T[], identifier: keyof T): T[] {
    for(const oItem of arr2){
        const itemInArr1 = 
            arr1.find(item => item[identifier] === oItem[identifier]);
        if(itemInArr1){
            for(const key in itemInArr1){
                itemInArr1[key] = oItem[key];
            }
        } else {
            arr1.push(oItem);
        }
    }
    return arr1;
}

console.log(mergeArray(array1,array2, 'id'));

Playground

This function loops through the items in array2 and verifies their presence within array1 based on the specified identifier.

Depending on whether the item exists in array1 or not, it will either be updated with information from array2, or the item from array2 is added to array1.

Answer 8

Below is an approach utilizing Generics:

const array1 =   [{
      'id': 1,
      'name': 'A'
    }, {
      'id': 2,
      'name': 'B'
    }, {
      'id': 3,
      'name': 'C'
    }]

const array2 =   [{
      'id': 1,
      'name': 'x'
    }, {
      'id': 2,
      'name': 'y'
    }]


function mergeArray<T>(arr1: T[], arr2: T[], identifier: keyof T): T[] {
    for(const oItem of arr2){
        const itemInArr1 = 
            arr1.find(item => item[identifier] === oItem[identifier]);
        if(itemInArr1){
            for(const key in itemInArr1){
                itemInArr1[key] = oItem[key];
            }
        } else {
            arr1.push(oItem);
        }
    }
    return arr1;
}

console.log(mergeArray(array1,array2, 'id'));

Playground

This function loops through the items in array2 and verifies their presence within array1 based on the specified identifier.

Depending on whether the item exists in array1 or not, it will either be updated with information from array2, or the item from array2 is added to array1.

Modify an array by incorporating values from another array that have a matching property

Answer №1

Answer №2

Answer №3

Answer №4

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