public class UserDto
{
	public int Id {get;set;}
	public string Name {get;set;}	
}

public class RowDto
{
	public IReadOnlyCollection<UserDto> Users {get;set;}
}

public class RowVm
{
	public IReadOnlyDictionary<int, string> Users {get;set;}
}

            CreateMap<RowDto, RowVm>()
                .ForMember(dest => dest.Users, opt => opt.MapFrom(src => src.Users.ToDictionary(key => key.Id, value => value.Name)))
                .PreserveReferences();