Is there a way to create a new array containing the first elements from each sub-array in another array?
[["1",2],["3",2],["6",2]]
The desired output:
['1', '3', '6']
My approach so far:
var newArray = []
for (i = 0; i < arrayToCompare.length - 1; i++) {
newArray.push(arrayToCompare[[0]])
}
You can easily achieve this by utilizing a simple map function along with destructuring the first element:
const arr = [["1", 2],["3", 2],["6", 2]]
console.log(arr.map(([e]) => e))The part in ([e]) before the => symbol implements destructuring to extract the parameter using array destructuring. This means that for each subarray processed by the map callback, e will hold the value of the first element within the subarray. In previous ES5 versions, the arrow function ([e]) => e would be equivalent to
function(entry) { return entry[0]; }If you find the concept difficult to grasp, seek efficiency, or simply prefer a more straightforward approach, you can always fall back on the reliable for loop, being sure to only store the first element of each subarray:
const arr = [["1", 2],["3", 2],["6", 2]]
const output = []
for (let i = 0; i < arr.length; i++) {
output.push(arr[i][0])
}
console.log(output)Give this a shot:
const array = [["1", 2], ["3", 2], ["6", 2]];
const result = array.map(item => {
return item[0];
})
console.log(result);To generate a new array containing items from the initial index, you can utilize Array.prototype.map():
var arr = [["1",2],["3",2],["6",2]]
var newArray = arr.map(i => i[0]);
console.log(newArray);This method also functions correctly
console.log(Object.keys(Object.fromEntries([["1", 2],["3", 2],["6", 2]])))Illustrated in this instance, the Object.fromEntries function constructs an object using an array of key/value pairs - interpreting the first element as a key and the second element as its corresponding value - resulting in an arrangement as displayed below:
{
"1": 2,
"3": 2,
"6": 2
}
Subsequently, Object.values is utilized to extract the keys from the previously created object, effectively removing the values while retaining only the keys.
Note: A different approach has been presented for achieving similar results
console.log(Array.from([["1", 2],["3", 2],["6", 2]], x=>x[0]))
Utilize the map function in combination with the shift method to retrieve the first element from each subarray.
Note: This approach may not be very efficient due to the use of the spread operator for each element.
const arr = [["1",2],["3",2],["6",2]];
const arrFirsts = arr.map(items => [...items].shift());
console.log(arrFirsts)
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