  In this study we consider relations between companies in Poland taking into
account common branches they belong to. It is clear that companies belonging to
the same branch compete for similar customers, so the market induces
correlations between them. On the other hand two branches can be related by
companies acting in both of them. To remove weak, accidental links we shall use
a concept of threshold filtering for weighted networks where a link weight
corresponds to a number of existing connections (common companies or branches)
between a pair of nodes.
