Map Javascript中arrays的数组的每个数组的第一个元素

Question

I have an array of arrays like this:

myData = [
          ["name1", 34.1, 43.1, 55.2],
          ["name2", 5.3, 23.6, 40.9],
          ["name3", 43.5, 77.8, 22.4]
         ];

I want to get an array containing only the first element of each array like this: ["name1", "name2", "name3"] .

I tried to do it like this but doesn't work:

var arrayTitle = myData.map(function(x) {
    return [myData[x][0]];
});

Any suggestions?

Answer 1

You could return just the first elementn of x , an element of the outer array.

 var myData = [["name1", 34.1, 43.1, 55.2], ["name2", 5.3, 23.6, 40.9], ["name3", 43.5, 77.8, 22.4]], arrayTitle = myData.map(function(x) { return x[0]; }); console.log(arrayTitle); 

Answer 2

Your x itself is an array. So you need not to touch myData again inside.

var arrayTitle = myData.map(function(x) {
    return x[0];
});

or with a traditional loop

 myData = [ ["name1", 34.1, 43.1, 55.2], ["name2", 5.3, 23.6, 40.9], ["name3", 43.5, 77.8, 22.4] ]; var arrayTitle = []; for(var k in myData) arrayTitle.push(myData[k][0]); console.log(arrayTitle); 

Answer 3

With your actual code return [myData[x][0]] , you are returning undefined , because x is the iterated item, so it's an array and not an index.

And using the wrapping [] is useless here, it's a destructing syntax, we don't need it here.

You should only return item[0] in each iteration:

var res = myData.map(function(arr) {
  return arr[0];
});

Demo:

 myData = [ ["name1", 34.1, 43.1, 55.2], ["name2", 5.3, 23.6, 40.9], ["name3", 43.5, 77.8, 22.4] ]; var res = myData.map(function(arr) { return [arr[x][0]]; }); console.log(res); 

Answer 4

This could be the shortest answer:

var res = myData.map(a => a[0])