Selecting closest subset of variables in r based on the highest and Lowest Values from another Variable

Question

I have this file:

id  egs aol pH  marm    fat PCQ
1   12  59  5.52    420 3   216
2   9   70  5.38    330 2   225
3   8   50  5.54    360 2   225
4   10  58  5.48