collapse: GRP – R documentation

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GRP

Fast Grouping / collapse Grouping Objects

Description

GRP performs fast, ordered and unordered, groupings of vectors and data frames (or lists of vectors) using radixorderv. The output is a list-like object of class 'GRP' which can be printed, plotted and used as an efficient input to all of collapse's fast statistical and transformation functions / operators, as well as to collap, BY and TRA.

fgroup_by is similar to dplyr::group_by but faster. It creates a grouped data frame with a 'GRP' object attached - for faster dplyr-like programming with collapse's fast functions.

There are also several conversion methods to convert to and from 'GRP' objects. Notable among these is GRP.grouped_df, which returns a 'GRP' object from a grouped data frame created with dplyr::group_by (or fgroup_by), and the duo GRP.factor and as.factor_GRP.

Usage

GRP(X, ...)

## Default S3 method:
GRP(X, by = NULL, sort = TRUE, decreasing = FALSE, na.last = TRUE,
    return.groups = TRUE, return.order = FALSE, call = TRUE, ...)

## S3 method for class 'factor'
GRP(X, ..., group.sizes = TRUE, drop = FALSE, return.groups = TRUE,
    call = TRUE)

## S3 method for class 'qG'
GRP(X, ..., group.sizes = TRUE, return.groups = TRUE, call = TRUE)

## S3 method for class 'pseries'
GRP(X, effect = 1L, ..., group.sizes = TRUE, return.groups = TRUE,
    call = TRUE)

## S3 method for class 'pdata.frame'
GRP(X, effect = 1L, ..., group.sizes = TRUE, return.groups = TRUE,
    call = TRUE)

## S3 method for class 'grouped_df'
GRP(X, ..., return.groups = TRUE, call = TRUE)

# Identify, get group names, and convert GRP object to factor
is.GRP(x)
GRPnames(x, force.char = TRUE)
as.factor_GRP(x, ordered = FALSE)

# Fast, class-agnostic version of dplyr::group_by for use with fast functions, see details
fgroup_by(X, ..., sort = TRUE, decreasing = FALSE, na.last = TRUE,
          return.order = FALSE)
      gby(X, ..., sort = TRUE, decreasing = FALSE, na.last = TRUE,
          return.order = FALSE)

# Get grouping columns from a grouped data frame created with dplyr::group_by or fgroup_by
fgroup_vars(X, return = "data")

# Ungroup grouped data frame created with dplyr::group_by or fgroup_by
fungroup(X, ...)

## S3 method for class 'GRP'
print(x, n = 6, ...)

## S3 method for class 'GRP'
plot(x, breaks = "auto", type = "s", horizontal = FALSE, ...)

Arguments

X

a vector, list of columns or data frame (default method), or a classed object (conversion / extractor methods).

x

a GRP object.

by

if X is a data frame or list, by can indicate columns to use for the grouping (by default all columns are used). Columns must be passed using a vector of column names, indices, or using a one-sided formula i.e. ~ col1 + col2.

sort

logical. This argument only affects character vectors / columns passed. If FALSE, these are not ordered but simply grouped in the order of first appearance of unique elements. This provides a slight performance gain if only grouping but not alphabetic ordering is required (argument passed to radixorderv).

ordered

logical. TRUE adds a class 'ordered' i.e. generates an ordered factor.

decreasing

logical. Should the sort order be increasing or decreasing? Can be a vector of length equal to the number of arguments in X / by (argument passed to radixorderv).

na.last

logical. If missing values are encountered in grouping vector/columns, assign them to the last group (argument passed to radixorderv).

return.groups

logical. Include the unique groups in the created GRP object.

return.order

logical. Include the output from radixorderv in the created GRP object.

group.sizes

logical. TRUE tabulates factor levels using tabulate to create a vector of group sizes; FALSE leaves that slot empty when converting from factors.

drop

logical. TRUE efficiently drops unused factor levels beforehand using fdroplevels.

call

logical. TRUE calls match.call and saves it in the final slot of the GRP object.

force.char

logical. Always output group names as character vector, even if a single numeric vector was passed to GRP.default.

effect

plm methods: Select which panel identifier should be used as grouping variable. 1L takes the first variable in the plm::index, 2L the second etc., identifiers can also be passed as a character string. More than one variable can be supplied.

return

an integer or string specifying what fgroup_vars should return. The options are:

Int.	String	Description
1	"data"	full grouping columns (default)
2	"unique"	unique rows of grouping columns
3	"names"	names of grouping columns
4	"indices"	integer indices of grouping columns
5	"named_indices"	named integer indices of grouping columns
6	"logical"	logical selection vector of grouping columns
7	"named_logical"	named logical selection vector of grouping columns

`n`	integer. Number of groups to print out.
`breaks`	integer. Number of breaks in the histogram of group-sizes.
`type`	linetype for plot.
`horizontal`	logical. `TRUE` arranges plots next to each other, instead of above each other.
`...`	for `fgroup_by`: unquoted comma-separated column names of grouping columns. Otherwise: arguments to be passed to or from other methods.

Details

GRP is a central function in the collapse package because it provides the key inputs to facilitate easy and efficient groupwise-programming at the C/C++ level: Information about (1) the number of groups (2) an integer group-id indicating which values / rows belong to which group and (3) information about the size of each group. Provided with these informations, collapse's Fast Statistical Functions pre-allocate intermediate and result vectors of the right sizes and (in most cases) perform grouped statistical computations in a single pass through the data.

The sorting and ordering functionality for GRP only affects (2), that is groups receive different integer-id's depending on whether the groups are sorted sort = TRUE, and in which order (argument decreasing). This in-turn changes the order of values/rows in the output of collapse functions. Note that sort = FALSE is only effective on character vectors, numeric grouping vectors will always produce ordered groupings.

Next to GRP, there is the function fgroup_by as a significantly faster alternative to dplyr::group_by. It creates a grouped data frame by attaching a 'GRP' object to a data frame. collapse functions with a grouped_df method applied to that data frame will yield grouped computations. Note that fgroup_by can only be used in combination with collapse functions, not with dplyr verbs such as summarize or mutate. The converse is not true, you can group data with dplyr::group_by and then apply collapse functions. Note also the fgroup_by is class-agnostic, i.e. the classes of the data frame or list passed are preserved, and all standard methods (like subsetting with `[` or print methods) apply to the grouped object. Apart from the class 'grouped_df' which is added behind any classes the object might inherit (apart from 'data.frame'), a class 'GRP_df' is added in front. This class responds to print method and subset (`[`) methods. Both first call the corresponding method for the object and then print / attach the grouping information. print.GRP_df prints below the object print one line indicating the grouping variables, followed, in square brackets, by the following information: [number of groups | average group size (standard-deviation of group sizes)].

GRP is an S3 generic function with one default method supporting vector and list input and several conversion methods:

The conversion of factors to 'GRP' objects by GRP.factor involves obtaining the number of groups calling ng <- fnlevels(f) and then computing the count of each level using tabulate(f, ng). The integer group-id (2) is already given by the factor itself after removing the levels and class attributes and replacing any missing values with ng + 1L. The levels are put in a list and moved to position (4) in the 'GRP' object, which is reserved for the unique groups. Going from factor to 'GRP' object thus only requires a tabulation of the levels, whereas creating a factor from a 'GRP' object using as.factor_GRP does not involve any computations, but may involve interactions if multiple grouping columns were used (which are then interacted to produce unique factor levels) or as.character conversions if the grouping column(s) were numeric (which are potentially expensive).

The method GRP.grouped_df takes the 'groups' attribute from a grouped data frame and converts it to a 'GRP' object. If the grouped data frame was generated using fgroup_by, all work is done already. If it was created using dplyr::group_by, a C routine is called to efficiently convert the grouping object.

Note: For faster factor generation and a factor-light class 'qG' which avoids the coercion of factor levels to character also see qF and qG.

Value

A list-like object of class ‘GRP’ containing information about the number of groups, the observations (rows) belonging to each group, the size of each group, the unique group names / definitions, whether the groups are ordered or not and (optionally) the ordering vector used to perform the ordering. The object is structured as follows:

List-index	Element-name	Content type	Content description
[[1]]	N.groups	`integer(1)`	Number of Groups
[[2]]	group.id	`integer(NROW(X))`	An integer group-identifier
[[3]]	group.sizes	`integer(N.groups)`	Vector of group sizes
[[4]]	groups	`unique(X)` or `NULL`	Unique groups (same format as input, sorted if `sort = TRUE`), or `NULL` if `return.groups = FALSE`
[[5]]	group.vars	`character`	The names of the grouping variables
[[6]]	ordered	`logical(2)`	`[1]- TRUE` if `sort = TRUE`, `[2]- TRUE` if `X` already sorted
[[7]]	order	`integer(NROW(X))` or `NULL`	Ordering vector from `radixorderv` or `NULL` if `return.order = FALSE` (the default)
[[8]]	call	`call()` or `NULL`	The `GRP()` call, obtained from `match.call()`, or `NULL` if `call = FALSE`

Examples

## default method
GRP(mtcars$cyl)
GRP(mtcars, ~ cyl + vs + am)      # Or GRP(mtcars, c("cyl","vs","am")) or GRP(mtcars, c(2,8:9))
g <- GRP(mtcars, ~ cyl + vs + am) # Saving the object
print(g)                          # Printing it
plot(g)                           # Plotting it
GRPnames(g)                       # Retain group names
fsum(mtcars, g)                   # Compute the sum of mtcars, grouped by variables cyl, vs and am

## Convert factor to GRP object and vice-versa
GRP(iris$Species)
as.factor_GRP(g)
 
## dplyr integration
library(dplyr)
mtcars %>% group_by(cyl,vs,am) %>% GRP    # Get GRP object from a dplyr grouped tibble
mtcars %>% group_by(cyl,vs,am) %>% fmean  # Grouped mean using dplyr grouping
mtcars %>% fgroup_by(cyl,vs,am) %>% fmean # Faster alternative with collapse grouping

mtcars %>% fgroup_by(cyl,vs,am)           # Print method for grouped data frame

collapse

Advanced and Fast Data Transformation

v1.5.3

GPL (>= 2) | file LICENSE

Authors

Sebastian Krantz [aut, cre], Matt Dowle [ctb], Arun Srinivasan [ctb], Laurent Berge [ctb], Dirk Eddelbuettel [ctb], Josh Pasek [ctb], Kevin Tappe [ctb], R Core Team and contributors worldwide [ctb], Martyn Plummer [cph], 1999-2016 The R Core Team [cph]

Initial release

2021-03-05

GRP