node_list
returns a data frame with one row per node, showing the
number of properties associated with a given node and a summary of
values for that node.
node_show
returns a data frame for a given node_id
listing all
properties associated with that node and a summary of values for each of
the properties.
node_select
returns a new object of class isatab containing only the
selected nodes.
prop_select
returns a new object of class isatab containing only the
selected property IDs (which may not be node IDs!).