collapse provides the following set of functions to efficiently work with lists of R objects:
Search and Identification
is.unlistable checks whether a (nested) list is composed of atomic objects in all final nodes, and thus unlistable to an atomic vector using unlist.
ldepth determines the level of nesting of the list (i.e. the maximum number of nodes of the list-tree).
has_elem searches elements in a list using element names, regular expressions applied to element names, or a function applied to the elements, and returns TRUE if any matches were found.
Subsetting
atomic_elem examines the top-level of a list and returns a sublist with the atomic elements. Conversely list_elem returns the sublist of elements which are themselves lists or list-like objects.
reg_elem and irreg_elem are recursive versions of the former. reg_elem extracts the 'regular' part of the list-tree leading to atomic elements in the final nodes, while irreg_elem extracts the 'irregular' part of the list tree leading to non-atomic elements in the final nodes. (Tipp: try calling both on an lm object). Naturally for all lists l, is.unlistable(reg_elem(l)) evaluates to TRUE…
get_elem extracts elements from a list using element names, regular expressions applied to element names, a function applied to the elements, or element-indices used to subset the lowest-level sub-lists. by default the result is presented as a simplified list containing all matching elements. With the keep.tree option however get_elem can also be used to subset lists i.e. maintain the full tree but cut off non-matching branches.
Splitting and Transposition
rsplit recursively splits a vector or data frame into subsets according to combinations of (multiple) vectors / factors - by default returning a (nested) list. If flatten = TRUE, the list is flattened yielding the same result as split. rsplit is also faster than split, particularly for data frames.
t_list efficiently transposes nested lists of lists, such as those obtained from splitting a data frame by multiple variables using rsplit.
Apply Functions
Unlisting / Row-Binding
unlist2d efficiently unlists unlistable lists in 2-dimensions and creates a data frame (or data.table) representation of the list (unlike unlist which returns an atomic vector). This is done by recursively flattening and row-binding R objects in the list (using data.table::rbindlist) while creating identifier columns for each level of the list-tree and (optionally) saving the row-names of the objects in a separate column. unlist2d can thus also be understood as a recursive generalization of do.call(rbind, l), for lists of vectors, data frames, arrays or heterogeneous objects.
| Function | Description | |
is.unlistable |
Checks if list is unlistable | |
ldepth |
Level of nesting / maximum depth of list-tree | |
has_elem |
Checks if list contains a certain element | |
get_elem |
Subset list / extract certain elements | |
atomic_elem |
Top-level subset atomic elements | |
list_elem |
Top-level subset list/list-like elements | |
reg_elem |
Recursive version of atomic_elem: Subset / extract 'regular' part of list |
|
irreg_elem |
Subset / extract non-regular part of list | |
rsplit |
Recursively split vectors or data frames / lists | |
t_list |
Transpose lists of lists | |
rapply2d |
Recursively apply functions to lists of data objects | |
unlist2d |
Recursively unlist/row-bind lists of data objects in 2D, to data frame or data.table |