weed out

weed out  {v.}

1. To remove what is unwanted, harmful, or not good enough from.

Mother weeded out the library because there were too many books.

Many colleges and universities weed out their freshman classes to make room for better students.

2. To take (what is not wanted) from a collection or group; remove (a part) for the purpose of improving a collection or group; get rid of.

The coach is weeding out the weak players this week.