How to select distinct rows in gridpanel based on userid using json

Hai i have used the below code:
string json = e.ExtraParams["Values"];

Dictionary<string,>[] companies = JSON.Deserialize<dictionary><string,>[]>(json);

StringBuilder sb = new StringBuilder();
sb.Append("<table cellspacing='15'>");
bool addHeader = true;
foreach (Dictionary<string,> row in companies)
{


foreach (KeyValuePair<string,> keyValuePair in row)
{
if (keyValuePair.Key.ToString().Equals("USER_ID"))
{
User_Id = keyValuePair.Value.ToString();
}
if (keyValuePair.Key.ToString().Equals("USER_ROLE"))
{
Session.Add("InvstTit", keyValuePair.Value.ToString());

InvstTit = keyValuePair.Value.ToString();


}
if (keyValuePair.Key.ToString().Equals("INVESTMENT_TITLE"))
{

Account_Name = keyValuePair.Value.ToString();


}
if (keyValuePair.Key.ToString().Equals("ACCOUNT_NAME"))
{

Date = keyValuePair.Value.ToString();


}
if (keyValuePair.Key.ToString().Equals("DOCUMENT_TYPE"))
{

Account = keyValuePair.Value.ToString();


}

//sb.Append("</td>");
}
user = User_Id + "@" + InvstTit + "@" + Account_Name + "@" + Account + "@" + Date;

if (!userslist.Contains(user))
{
userslist.Add(user);
}

}

now i here in userslist i am getting all the selected row values. now i need to get row values based on distinct user_id.how can i achieve this by using linq ?