fast-grouping-ordering {collapse}

Fast Grouping and Ordering

Description

collapse provides the following functions to efficiently group and order data:

• radixorder, provides fast radix-ordering through direct access to the method order(..., method = "radix"), as well as the possibility to return some attributes very useful for grouping data and finding unique elements. radixorderv exists as a programmers alternative. The function roworder(v) efficiently reorders a data frame based on an ordering computed by radixorderv.

• group provides fast grouping in first-appearance order of rows, based on a hashing algorithm in C. Objects have class 'qG', see below.

• GRP creates collapse grouping objects of class 'GRP' based on radixorderv or group. 'GRP' objects form the central building block for grouped operations and programming in collapse and are very efficient inputs to all collapse functions supporting grouped operations.

• fgroup_by provides a fast replacement for dplyr::group_by, creating a grouped data frame (or data.table / tibble etc.) with a 'GRP' object attached. This grouped frame can be used for grouped operations using collapse's fast functions.

• fmatch is a fast alternative to match, which also supports matching of data frame rows.

• funique is a faster version of unique. The data frame method also allows selecting unique rows according to a subset of the columns. fnunique efficiently calculates the number of unique values/rows. fduplicated is a fast alternative to duplicated. any_duplicated is a simpler and faster alternative to anyDuplicated.

• fcount computes group counts based on a subset of columns in the data, and is a fast replacement for dplyr::count. fcountv is a programmers version of the function.

• qF, shorthand for 'quick-factor' implements very fast factor generation from atomic vectors using either radix ordering method = "radix" or hashing method = "hash". Factors can also be used for efficient grouped programming with collapse functions, especially if they are generated using qF(x, na.exclude = FALSE) which assigns a level to missing values and attaches a class 'na.included' ensuring that no additional missing value checks are executed by collapse functions.

• qG, shorthand for 'quick-group', generates a kind of factor-light without the levels attribute but instead an attribute providing the number of levels. Optionally the levels / groups can be attached, but without converting them to character. Objects have a class 'qG', which is also recognized in the collapse ecosystem.

• fdroplevels is a substantially faster replacement for droplevels.

• finteraction is a fast alternative to interaction implemented as a wrapper around as_factor_GRP(GRP(...)). It can be used to generate a factor from multiple vectors, factors or a list of vectors / factors. Unused factor levels are always dropped.

• groupid is a generalization of data.table::rleid providing a run-length type group-id from atomic vectors. It is generalization as it also supports passing an ordering vector and skipping missing values. For example qF and qG with method = "radix" are essentially implemented using groupid(x, radixorder(x)).

• seqid is a specialized function which creates a group-id from sequences of integer values. For any regular panel dataset groupid(id, order(id, time)) and seqid(time, order(id, time)) provide the same id variable. seqid is especially useful for identifying discontinuities in time-sequences.

• timeid is a specialized function to convert integer or double vectors representing time (such as 'Date', 'POSIXct' etc.) to factor or 'qG' object based on the greatest common divisor of elements (thus preserving gaps in time intervals).

Table of Functions

Function / S3 Generic		Methods		Description
radixorder(v)		No methods, for data frames and vectors		Radix-based ordering + grouping information
roworder(v)		No methods, for data frames incl. pdata.frame		Row sorting/reordering
group		No methods, for data frames and vectors		Hash-based grouping + grouping information
GRP		default, GRP, factor, qG, grouped_df, pseries, pdata.frame		Fast grouping and a flexible grouping object
fgroup_by		No methods, for data frames		Fast grouped data frame
fmatch		No methods, for vectors and data frames		Fast matching
funique, fnunique, fduplicated, any_duplicated		default, data.frame, sf, pseries, pdata.frame, list		Fast (number of) unique values/rows
fcount(v)		Internal generic, supports vectors, matrices, data.frames, lists, grouped_df and pdata.frame		Fast group counts
qF		No methods, for vectors		Quick factor generation
qG		No methods, for vectors		Quick grouping of vectors and a 'factor-light' class
fdroplevels		factor, data.frame, list		Fast removal of unused factor levels
finteraction		No methods, for data frames and vectors		Fast interactions
groupid		No methods, for vectors		Run-length type group-id
seqid		No methods, for integer vectors		Run-length type integer sequence-id
timeid		No methods, for integer or double vectors		Integer-id from time/date sequences

See Also

Collapse Overview, Data Frame Manipulation, Time Series and Panel Series