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 functions, operators, as well as collap, BY and TRA.
fgroup_by is similar to dplyr::group_by but faster. It creates a 'grouped_df', but 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. The most important of these is GRP.grouped_df, which returns a 'GRP' object from a 'grouped_df' created with fgroup_by or dplyr::group_by.
GRP(X, ...)# S3 method for default
GRP(X, by = NULL, sort = TRUE, decreasing = FALSE, na.last = TRUE,
return.groups = TRUE, return.order = FALSE, ...)
# S3 method for factor
GRP(X, ...)
# S3 method for qG
GRP(X, ...)
# S3 method for pseries
GRP(X, effect = 1L, ...)
# S3 method for pdata.frame
GRP(X, effect = 1L, ...)
# S3 method for grouped_df
GRP(X, ...)
# Identify, get group names, and convert GRP object to factor
is.GRP(x)
group_names.GRP(x, force.char = TRUE)
as.factor.GRP(x, ordered = FALSE)
# Fast 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)
# This gets grouping columns from a grouped_df created with dplyr::group_by or fgroup_by
fgroup_vars(X, return = "data")
# S3 method for GRP
print(x, n = 6, ...)
# S3 method for GRP
plot(x, breaks = "auto", type = "s", horizontal = FALSE, ...)
a vector, list of columns or data.frame (default method), or a classed object (conversion/extractor methods).
a GRP object.
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.
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).
logical. TRUE adds a class 'ordered' i.e. generates an ordered factor.
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).
logical. if missing values are encountered in grouping vector/columns, assign them to the last group (argument passed to radixorderv).
logical. include the unique groups in the created 'GRP' object.
logical. include the output from radixorderv in the created 'GRP' object.
logical. Always output group names as character vector, even if a single numeric vector was passed to GRP.default.
plm methods: Select which panel identifier should be used as grouping variable. 1L means first variable in the plm::index, 2L the second etc.. More than one variable can be supplied.
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 |
integer. Number of groups to print out.
integer. Number of breaks in the histogram of group-sizes.
linetype for plot.
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.
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) |
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 group, there is the function fgroup_by as a significantly faster alternative to dplyr::group_by. It creates a grouped tibble 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.
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 <- flevels(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 tibble and converts it to a 'GRP' object. If the grouped tibble 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.
# NOT RUN {
## default method
GRP(mtcars$cyl)
GRP(mtcars, ~ cyl + vs + am) # or GRP(mtcars, c("cyl","vs","am")) or GRP(mtcars, c(2,8:9))
g <- GRP(mtcars, ~ cyl + vs + am) # saving the object
plot(g) # plotting it
group_names.GRP(g) # retain group names
fsum(mtcars, g) # compute the sum of mtcars, grouped by variables cyl, vs and am.
## convert factor to GRP object
GRP(iris$Species)
## 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
# }
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