group_by) and create new site or horizon level attributes
summarize() is a function used for summarizing SoilProfileCollections. 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.
A set of (named) comma-delimited R expressions that resolve to a summary value. e.g
groupmean = mean(clay, na.rm = TRUE)
A data.frame with one row per level in the grouping variable, and one column for each summary