changes from the novel

I'm only halfway through the novel and there are too many changes to mention and no doubt there'll be even more in the second half.
I already knew that the movie portrays Tom as being a lot more oppressed and vulnerable than in the novel, in which he's already a con artist in New York and displaying psychopathic tendencies even before San Remo.
What I didn't know, though, and it's the most startling of all the changes so far, is that Tom actually knew Dickie, having hung out with him and some mutual friends on a couple of occasions.
It's one of these mutual acquaintances who recommends Tom for "the job" to Herbert Greenleaf, who actively approaches Tom about this (as opposed to it coming from a misunderstanding over the Princeton jacket).
It's a very curious change - I guess it makes it easier to follow if he's blagging about knowing Dickie from the beginning. Next time I watch though I'm going to keep this in mind - the "movie" Tom probably at least knew people who knew Dickie - he has associates at Princeton, hence him borrowing the jacket and playing piano at that posh event. Maybe they had actually been in the same room or at the same event at least once in New York that Dickie wouldn't remember, hence Tom going with the "i was at princeton with you" story.