collapse (version 1.5.0)

A8-list-processing: List Processing

Description

collapse provides the following set of functions to work with lists of R objects:

• Search and Identification

  • is.regular checks whether an R object is either atomic or a list. A (nested) list composed of regular objects at each level of the list-tree is unlistable to an atomic vector - checked by is.unlistable.

  • 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

  • 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.

• Apply Functions

  • rapply2d is a recursive version of lapply with two key differences to rapply: (1) Data frames are considered as atomic objects, not as (sub-)lists, and (2) the result is not simplified.

• 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.

Table of Functions

Function		Description
is.regular		function(x) is.atomic(x) || is.list(x)
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
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

See Also

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