Perform summaries on groups (from group_by) and create new site or horizon level attributes
Source: R/summarize.R
summarizeSPC.Rdsummarize() is a function used for summarizing a SoilProfileCollection object. Specify the groups using the group_by verb, and then (named) expressions to evaluate on each group. The result is a data.frame with one row per categorical level in the grouping variable and one column for each summary variable.