extrema_by: Find rows with extrema in specific columns

In table.express: Build 'data.table' Expressions with Data Manipulation Verbs

Find rows with extrema in specific columns

Description

Find rows with maxima/minima in given columns.

Usage

max_by(.data, .col, ...)

## S3 method for class 'ExprBuilder'
max_by(
  .data,
  .col,
  ...,
  .some = FALSE,
  .chain = getOption("table.express.chain", TRUE)
)

## S3 method for class 'data.table'
max_by(.data, .col, ..., .expr = FALSE)

min_by(.data, .col, ...)

## S3 method for class 'ExprBuilder'
min_by(
  .data,
  .col,
  ...,
  .some = FALSE,
  .chain = getOption("table.express.chain", TRUE)
)

## S3 method for class 'data.table'
min_by(.data, .col, ..., .expr = FALSE)

Arguments

.data	An instance of ExprBuilder.
.col	A character vector indicating the columns that will be searched for extrema.
...	Optionally, columns to group by, either as characters or symbols.
.some	If TRUE the rows where any of the columns specified in .col have extrema are returned.
.chain	Logical. Should a new frame be automatically chained to the expression if the clause being set already exists?
.expr	If the input is a data.table and .expr is TRUE, an instance of EagerExprBuilder will be returned. Useful if you want to add clauses to j, e.g. with mutate-table.express.

Details

These verbs implement the idiom shown here by leveraging nest_expr(). The whole nested expression is assigned to i in the data.table's frame. It is probably a good idea to use this on a frame that has no other frames preceding it in the current expression, given that nest_expr() uses the captured data.table, so consider using chain() when needed.

Several columns can be specified in .col, and depending on the value of .some, the rows with all or some extrema are returned, using & or | respectively. Depending on your data, using more than one column might not make sense, resulting in an empty data.table.

Examples

data("mtcars")

data.table::as.data.table(mtcars) %>%
    max_by("mpg", "vs")

table.express documentation built on April 3, 2023, 5:43 p.m.