jQuery Grid Plugin - jqGrid

Hello, 

I have my two variable

my variable mydata1 have 30 rows 

my variable mydata2 have 5 rows

 And I want to switch these two data in my default jqGrid option. Actuallay default options are:

datatype: 'local',

data: mydata1

but When I try to change data(with a click event) by another variable mydata2 who have 5 rows… In the GRID just 5 first rows are changing…the rest are always there…. Why there is this reaction  please ? I need to change data completly… 

This is click event:

$('.changeDate').click(function() {

grid.setGridParam({

datatype : 'local',

data : mydata2

}).trigger("reloadGrid");

});