get in(to) single file

1. To form into a line one person or thing in width. OK, children, please get in single file and make your way to the auditorium. The ducklings got into single file behind their mother and made their way across the road. Cyclists are reminded to please get into single file on roads to avoid obstructing traffic.

2. To arrange people or things into such a line. In this usage, a noun or pronoun is used between "get" and "in(to)." I'd like you to get all the boxes in single file. It will make it easier to inspect them. The officer got the prisoners into single file and then loaded them onto the prison transport. Can you get all your students into single file? That way, they can come in and take their school pictures one at a time and speed up the whole process.