Append extra data in the chart after selecting new item from a dropdown in JSF

Append extra data in the chart after selecting new item from a dropdown in
JSF

I am using highcharts to generate chart based on selecting items in a
dropdown list. When I select first item from the dropdown it is showing
correct data. When I select second item from the dropdown it is also
showing correct data. But when I select first item from the dropdown again
then it is appending few data with the first chart.
For example: first dropdown item has 1000 data points. Second dropdown
item has 1500 data points. When I select first item of the dropdown after
selecting second item of the dropdown then the first 1000 data points are
correct but it also append 500 abnormal data in the chart. Because the
second item hase 1500 data points in total. The first item always get teh
size of the second item when I select second item.
How can I fix that?