  Minijets provide useful information on parton interactions in the low
transverse-momentum (low-$p_T$) region. Because minijets produce clusters, we
study the clustering properties of produced particles in high-energy $pp$
collisions as a first step to identify minijets. We develop an algorithm to
find clusters by using the k-means clustering method, in conjunction with a
k-number (cluster number) selection principle in the space of pseudorapidity
and azimuthal angles. We test the clustering algorithm using events generated
by PYTHIA 8.1, for $pp$ collision at $\sqrt{s}=200$ GeV. We find that
clustering of low-$p_T$ hadrons occurs in high multiplicity events. However
similar clustering properties are also present for particles produced randomly
in a finite pseudorapidity and azimuthal angle space. To distinguish the
dynamics from random generations of events, it is necessary to examine the
correlation between particles and between clusters. We find that the
correlations between clusters may provide a useful tool to distinguish the
underlying dynamics of the reaction mechanism.
