Define two ways in which you might define the proximity among a group of objects.

Proximity is typically defined between a pair of objects.

Two examples are the following: (i) based on pairwise proximity, i.e.,
minimum pairwise similarity or maximum pairwise dissimilarity, or (ii)
for points in Euclidean space compute a centroid (the mean of all the
points—see Section 8.2) and then compute the sum or average of the
distances of the points to the centroid.