how to merge gridview rows dynamically

Hello everyone,

I want to merge gridview rows dynamically but my data comes from third party webservice so i m binding Ilist object to gridview1.datasource and it will also change condition wise like 

if(value=2)
{ merge two rows}
else if(value=3}
{merge three rows}
else if(value=4)
{merge four rows}

plz help me its urgent....

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