The phrase "a first group of" is correct and usable in written English.
It can be used when introducing or categorizing a specific set of items or individuals within a larger context.
Example: "In our study, we analyzed a first group of participants who met the criteria for inclusion."
Alternatives: "an initial set of" or "a primary group of".
Mr. Ajan said a first group of strangers visited the house eight days ago.
Ms. Trimarco said Venezuela had granted formal refugee status to a first group of 47 Colombians.
Shortly afterwards, a first group of more than 350 children were released by armed groups.
General Myers said a first group of prisoners would be flown soon to a new high-security jail at the American naval base at Guantánamo Bay, Cuba.
Earlier this month, the Guardian was among a first group of foreign journalists and Greenpeace activists who were invited to see how they live and operate.
Moses Josiah, a leading gospel-musical sawyer, was playing & pleased-looking staff people were leading a first group of children through the exhibits.
Police used teargas at noon when a first group of protesters, many of them workers who had come in from provincial towns, tried to break into the parliament.
The company has trained a first group of 150 militia members and is drilling a second group of equal size, an official familiar with the company's operations said.
A first group of proactive countries can usefully emerge, but an à la carte Europe, which would see some claiming the advantages of the EU without complying with the obligations that come with them, is not a conceivable option.
The protest will begin at about 11am on Saturday morning when a first group of 100 activists will gather at the gates of the White House, an area that is supposed to be kept clear, and wait to be arrested.
A first group of heirs had been tracked down by a genealogist and a notary, who was also working for the state, and to whom all the non-Austrian residents were required to pay a 40% contingent fee.
