循环通过Json对象

Question

I am trying to only print a unique value of 'sum' by doing a compare at the end of the loop, but I'm seeing that every time it does a compare it has already moved on to the next element and therefore when its comparing the two values they're always the same. Is there another way to do this?

 $(document).ready(function(){
    $.getJSON('XML.php', function(data) {
        JSON.stringify(data);
        var prevCardCode = '';

        $.each( data, function(index, element){
            var prevCardCode = element['CardCode'];

            if (!(element['CardCode'] == prevCardCode)) {

                var sum = element['payment_sum'] + '<br/>';
                $('#showdata').append(sum);
                }
                alert(element['CardCode'] + 'compare' + prevCardCode);
        });

    });
});

Answer 1

You need to move the prevCharCode assignment to the end of the loop and remove the var in front of it:

var prevCardCode = '';
$.each( data, function(index, element) {
    if (!(element['CardCode'] == prevCardCode)) {
        // your code...
    }

    prevCardCode = element['CardCode'];
});

Answer 2

The var keyword doesn't belong within the each in this case, and you need to move it to after the comparison.

var prevCardCode = '';
$.each(data, function(index, element) {
    if (!(element['CardCode'] == prevCardCode)) {
        var sum = element['payment_sum'] + '<br/>';
        $('#showdata').append(sum);
    }
    alert(element['CardCode'] + 'compare' + prevCardCode);
    prevCardCode = element['CardCode'];
});​

If the var is left in place before prevCardCode , it will never set the one defined outside of the $.each and will not carry over to the next iteration of $.each .

Answer 3

prevCardCode is not the precedent element but the current... Then you compare current with current...

If you want to compare precedent element with current, you should use a while or a do while.

var i = 1;
var precedentEl = array[0];

while (i < array.length) {

   // Do some stuff like compare current and precedent

   precedentEl = array[i];
   i++;
}

Secondly, you call XML.php which return json... It's sound strange...