i have this 2 array,
const firstArray = [
{
key: 'a',
value: 'a'
},
{
key: 'b',
value: 'b'
},
{
key: 'c',
value: 'c'
}
]
const secondArray = [
{
key: 'b',
value: 'd'
},
{
key: 'c',
value: 'e'
}
]
i want to merge these 2 array, and if a same key found on second array the second array value will replace first array value
the new array should look like this
const expectedArray = [
{
key: 'a',
value: 'a'
},
{
key: 'b',
value: 'd'
},
{
key: 'c',
value: 'e'
}
]
As I see lodash in your tags, I assume you want to use it.
You can use something like this:
var merged = _(firstArray)
.concat(secondArray)
.groupBy("key")
.map(_.spread(_.merge))
.value();
It basically groups all objects with the same key into an array with groupBy("key"), then flattens out each array of values merging them and taking the last one with .map(_.spread(_.merge)).
I suggest commenting out the final likes and see all the intermediate steps if you want to fully understand the process, it's interesting!
const firstArray = [{
key: 'a',
value: 'a'
},
{
key: 'b',
value: 'b'
},
{
key: 'c',
value: 'c'
}
]
const secondArray = [{
key: 'b',
value: 'd'
},
{
key: 'c',
value: 'e'
}
]
var merged = _(firstArray)
.concat(secondArray)
.groupBy("key")
.map(_.spread(_.merge))
.value();
console.log(merged);<script src="https://cdn.jsdelivr.net/lodash/4.13.1/lodash.min.js"></script>
_.spread(_.merge). so the spread will run merge for each description, and for key a since its just have one object inside, its just return same object, but for key b and c, because it have 2 object inside each key, it will be return last object. am i right?
key value so it does not change, but for description (and more fields if there are) it will merge them all and take the last value.Solution without lodash is to iterate through the second array and just look for matches.
If there's no match, push the item to the first array.
If there's a match, replace the item in the first array with the one from the second array.
const mergedArray = [...firstArray]
secondArray.forEach(newItem => {
const matchIndex = mergedArray.findIndex(prevItem => prevItem.key === newItem.key)
if (matchIndex === -1) {
mergedArray.push(newItem)
} else {
mergedArray[matchIndex] = newItem
}
})
const mergedArray = [...secondArray, ...firstArray];
const lengthOfUniqueArray = new Set(mergedArray.map((item) => item.key)).size;
const expectedArray = newArray.slice(0, lengthOfUniqueArray);
expectedArray will be what you want.
key to be in the expectedArray, which is not what was asked here.You can concat, reverse, can all unique elements by key, and then reverse back:
const { flow, concat, reverse, uniqBy } = _
const mergeArrays = flow(
concat,
reverse,
arr => uniqBy(arr, 'key'),
reverse
)
const firstArray = [{"key":"a","value":"a"},{"key":"b","value":"b"},{"key":"c","value":"c"}]
const secondArray = [{"key":"b","value":"d"},{"key":"c","value":"e"}]
var merged = mergeArrays(firstArray, secondArray)
console.log(merged)<script src="https://cdn.jsdelivr.net/lodash/4.13.1/lodash.min.js"></script>
