Auto Calculate form fields value using jQuery calculation plugin

I am building a form that will automatically calculate the values entered by a user ideally using jQuery/javascript, i am not sure how to do this but have a general idea of the logic required (i am no expert so feel free to correct me) - I have created a dummy image to help explain what I am trying to do.

http://i.sta开发者_如何学Pythonck.imgur.com/WScNO.png

I have a single form, which has many input fields automatically calculate the total amount for each table provided it has been selected. Using jQuery - I would expect the logic to be something like - i) Find the input field element ii) Find all the text fields within the table that have a value iii) Add these together and display in the 'total' form field

While i'm ok on the PHP, javascript is something I still get confused with at times - I would appreciate any help on doing this, and if possible a quick overview to help me learn from the code.

Thanks in advance

Try this:http://jsfiddle.net/Ajkkb/26/

<div>
    <input  name="r"  class="rate" type="text" maxlength="255" size="5" value=""/> 
    <input  name="p" class="pack" type="text" maxlength="255" size="5" value=""/>
    <input  name="b" class="bag" type="text" maxlength="255" size="5" value=""/> 
    <input  name="w" class="weight" type="text" maxlength="255" size="5" value=""/> 
    <span  class="amount"></span> 
</div>
<div>
    <input  name="r"  class="rate" type="text" maxlength="255" size="5" value=""/> 
    <input  name="p" class="pack" type="text" maxlength="255" size="5" value=""/>
    <input  name="b" class="bag" type="text" maxlength="255" size="5" value=""/> 
    <input  name="w" class="weight" type="text" maxlength="255" size="5" value=""/>
    <span class="amount"></span> 
</div>
<div>
    <input  name="r"  class="rate" type="text" maxlength="255" size="5" value=""/> 
    <input  name="p" class="pack" type="text" maxlength="255" size="5" value=""/>
    <input  name="b" class="bag" type="text" maxlength="255" size="5" value=""/> 
    <input  name="w" class="weight" type="text" maxlength="255" size="5" value=""/>
    <span class="amount"></span> 
</div>
<div class="total_amount">total</div>



$(document).ready(function() {
    $('input[name=r],input[name=p]').change(function(e) {
        var total = 0;
        var $row = $(this).parent();
        var rate = $row.find('input[name=r]').val();
        var pack = $row.find('input[name=p]').val();
        total = parseFloat(rate * pack)*100;
        //update the row total
        $row.find('.amount').text(total);

        var total_amount = 0;
        $('.amount').each(function() {
            //Get the value
            var am= $(this).text();
            console.log(am);
            //if it's a number add it to the total
            if (IsNumeric(am)) {
                total_amount += parseFloat(am, 10);
            }
        });
        $('.total_amount').text(total_amount);
    });
});

//isNumeric function Stolen from: 
//http://stackoverflow.com/questions/18082/validate-numbers-in-javascript-isnumeric

function IsNumeric(input) {
    return (input - 0) == input && input.length > 0;
}