Get data attribute inside multiple children - performance

Question

I have this issue: Multiple classes with several span inside of each class and want to extract all data attributes of the first class.
<div class="parent_class">
<span data-year="a_1">Data</span>
<span data-make="b_1">Data</span>
<span data-model="c_1">Data</span>
<span data-motor="d_1">Data</span>
</div>
<div class="parent_class">
<span data-year="a_2">Data 2</span>
<span data-make="b_2">Data 2</span>
<span data-model="c_2">Data 2</span>
<span data-motor="d_2">Data 2</span>
</div>
I have made several tries and just got the first data attribute with not problem.
var year_response = $('.parent_class:first span').data('year');
Response:
year_response = a1;
But when I tried for the make and other data attribute I got undefined
Actual:
var make_response = $('.parent_class:first span').data('make');
**Response:
make_response = undefined;**
Desire:
var make_response = $('.parent_class:first span').data('make');
**Response:
make_response = b_1;**

Answer 1

How about just fetching all data attributes of the spans as objects and mapping them to an array :
var data = $.map($('.parent_class:first span'), function(el) {
return $(el).data();
});
FIDDLE
or an object if all the data attributes are different :
var data = {};
$.each($('.parent_class:first span'), function(i, el) {
$.each($(el).data(), function(k,v) {data[k] = v});
});
FIDDLE

Answer 2

You are telling it to get the first span, but the you want the second span (the one with make). What about getting the first with the make data attribute?
console.log($('.parent_class > span[data-make]:first').data('make'));
You could also select the nth element with the nth-child selector:
console.log($('.parent_class > span:nth-child(2)').data('make'));