That is important to know. And raw foodists want others to believe as they came to believe, that any food cooked has its nutrients ruined. That does not have basis, showing raw food is healthier, like whole food that is plant-based does. They are not fully compatible ways. I will go with what has fully convincing studies, if any studies ever are, behind it.
If my memory serves me right (which is always questionable), the raw foodies actually have a point. About cooking reducing the nutritional value of food. However, cooking also makes some nutrients more absorbable and available. I remember seeing a chart or list a while back. If I see it again I'll post it here. or maybe someone else will.
Well, I can't find the chart but here is a couple of things that I gleaned.
"Cooked carrots, spinach, mushrooms, asparagus, cabbage, peppers and many other vegetables also supply more antioxidants, such as carotenoids and ferulic acid, to the body than they do when raw...." (1)
Broccoli is the most often cited veggie to eat raw. cooking veggies usually reduces the vitamins and minerals in a veggie. Since many vitamins are water soluble they leech out when cooking. One of the vitamins most often mentioned was vitamin C which is found in everything anyway so you probably don't need to worry about it.
The one thing that almost every article agreed on is that eating veggies is good no matter if you cook them or not.