The phrase "a vast group" is correct and usable in written English.
It can be used to describe a large number of people or things that are gathered or categorized together.
Example: "The conference attracted a vast group of experts from various fields, all eager to share their knowledge."
Alternatives: "a large crowd" or "an extensive assembly".
The opener looked at the vertebrates – a vast group taking in mammals, birds, fish, amphibians and reptiles.
I envisioned a vast group of people, men mostly, who pursued a particular kind of frictionless life.
For Nissim's army buddies, 8200 is Israeli hi-tech's old school tie, opening doors to a vast group of like-minded and similarly-trained entrepreneurs.
We have created the Debt Generation, a vast group of people in whom a mental switch was tripped while they were trying to get an education.
The nematodes, in particular, are a vast group of tiny worms that are both ubiquitous and virtually unacknowledged outside the laboratory.
But as a black comedy set in a dystopian Britain being destroyed by a vast group hallucination, it may now take on more profound and pressing connotations following last night's result.
All anyone knows about this particular mystery is its background — the student riots of May, 1968, when France was either within a breath of armed revolution or merely involved in a vast group-therapy session.
Now in its sixth year, and such a huge international success, it would be forgivable if the entire London art scene just imploded into a vast group-hug of self-love.
And those, like the intentions of any vast group, can be difficult to assess.
A gap remains for the vast group in the middle: 90 % of the elderly still relied on familial care in 2012 (Zhang 2012).
Last week, the World Youth Conference in Mexico provided a platform for representatives of this vast group to voice their opinions.
