如何添加這個嵌套數組的第一個元素

Question

我有這個嵌套數組

let thirarray = [
    [2, 3, 4],
    [5, 6, 7, 8],
    [9, 10],
];

我想要做的是添加每個數組的第一個元素所以基本上添加 2+5+9=16 我知道我可以像這樣訪問每個元素

//this is how i can access the first element of each array
console.log(thirarray[0][0]);
console.log(thirarray[1][0]);
console.log(thirarray[2][0]);

我知道我可以使用嵌套循環訪問所有這樣的元素

let suminsidearrays = 0;

for (i = 0; i < thirarray.length; i++) {
    for (let j = 0; j < thirarray[i].length; j++) {
        console.log(thirarray[i][j]);
        suminsidearrays += thirarray[i][j];
        console.log(suminsidearrays);

    }
}

所以我的問題是如何添加每個數組的第一個元素？

Answer 1

這將對主數組中每個數組的第一個元素求和。

 const array = [[2, 3, 4],[5, 6, 7, 8],[9, 10]] let sum = array.reduce((a,c)=>a+c[0],0) console.log(sum)

更新評論中的新模式要求。

 const array = [[2, 3, 4],[5, 6, 7, 8],[9, 10, 11]] let i = 0, sum = array.reduce((a,c)=>a+c[i++],0) console.log(sum)

Answer 2

最簡單的方法

 let thirarray = [[2, 3, 4],[5, 6, 7, 8],[9, 10]]; var res=0 thirarray.forEach(a=>res+=a[0]) console.log(res)

Answer 3

我只想補充一點，我能夠使用從@holydragon 學到的東西來解決它。 所以這就是我所做的

let fourthrarray = [
    [20, 30, 40],
    [50, 60, 70, 80],
    [90, 100, 110, 120, 130],
];

let nextindexposition = 0;
let nextto = 0;
let sumeelsegundo = 0;

for (let i = 0; i < fourthrarray.length; i++) {
    //this will allow me to see the 1st index position from each array
    //i should expect to see 20,50,90
    sumeelsegundo = fourthrarray[i][0];
   //this will add the first index position of each array expected output will be 160
    sumeelsegundo += fourthrarray[i][0];
    console.log(sumeelsegundo);
   //in order to add the next index position from each array i used two variable
  //one that will store the result and the other one that will increase the index 
  //position by one on every iteration. this one will allow me to see the elements
 //that will be added. expected elements will be 20,60,110
    nextto = fourthrarray[i][nextindexposition++];
 //this will be adding the elements expected output expected output 190
    nextto += fourthrarray[i][nextindexposition++];
    console.log(nextto);

}

只是為了澄清一下這個解決方案適用於添加數字，如果我想相乘，我只需將變量 nextto 的起始值從 0 更改為 1。