从地图中获取React中的唯一值？

Question

我想从下面的代码中获取countryCode的唯一值。

public async Task AsyncTask()
{
    //start the Tasks so they run concurrently
    var mainFormTask = Task.Run(() => CreateAppForm());
    var createTableTask = Task.Run(() => CreateTables());

    //await the Tasks and get the results
    Form MainForm = await mainFormTask;
    DataTable[] MasterTables = await createTableTask;
}

Answer 1

{
const countryCodes = [];
respDcNumber.map((user, i) => {
    // Only return if it's not already in the list
    if (!countryCodes.includes(user.countryCode)) {
        countryCodes.push(user.countryCode);
        return <MenuItem value={user.countryCode}>{user.countryCode}</MenuItem>;
    }
    return null;
});
}

Answer 2

尝试使用Set这样的方法来获取唯一的countryCode值并将其映射。

{
    [...new Set(uniqueUsers.map(x=>x.countryCode))].map(code =>
    <MenuItem key={code.countryCode} value={code.countryCode}>{code.countryCode}</MenuItem>)
}