TableTree (or related class). A TableTree object representing a populated table.
path_fun
function. Function to transform paths into single-string row/column names.
value_fun
function. Functiont to transform cell values into cells of the data.frame. Defaults to collapse_values which
creates strings where multi-valued cells are collapsed together, separated by |.
Value
A data frame of tt's cell values (processed by value_fun,
with columns named by the full column
paths (processed by path_fun and an additional row_path column
with the row paths (processed by by path_fun).