slice.dtplyr_step: Subset rows using their positions

In dtplyr: Data Table Back-End for 'dplyr'

Subset rows using their positions

Description

These are methods for the dplyr slice(), slice_head(), slice_tail(), slice_min(), slice_max() and slice_sample() generics. They are translated to the i argument of ⁠[.data.table⁠.

Unlike dplyr, slice() (and slice() alone) returns the same number of rows per group, regardless of whether or not the indices appear in each group.

Usage

## S3 method for class 'dtplyr_step'
slice(.data, ..., .by = NULL)

## S3 method for class 'dtplyr_step'
slice_head(.data, ..., n, prop, by = NULL)

## S3 method for class 'dtplyr_step'
slice_tail(.data, ..., n, prop, by = NULL)

## S3 method for class 'dtplyr_step'
slice_min(.data, order_by, ..., n, prop, by = NULL, with_ties = TRUE)

## S3 method for class 'dtplyr_step'
slice_max(.data, order_by, ..., n, prop, by = NULL, with_ties = TRUE)

Arguments

.data	A lazy_dt().
...	For slice(): <data-masking> Integer row values. Provide either positive values to keep, or negative values to drop. The values provided must be either all positive or all negative. Indices beyond the number of rows in the input are silently ignored. For ⁠slice_*()⁠, these arguments are passed on to methods.
.by, by	<tidy-select> Optionally, a selection of columns to group by for just this operation, functioning as an alternative to group_by(). For details and examples, see ?dplyr_by.
n, prop	Provide either n, the number of rows, or prop, the proportion of rows to select. If neither are supplied, n = 1 will be used. If n is greater than the number of rows in the group (or prop > 1), the result will be silently truncated to the group size. prop will be rounded towards zero to generate an integer number of rows. A negative value of n or prop will be subtracted from the group size. For example, n = -2 with a group of 5 rows will select 5 - 2 = 3 rows; prop = -0.25 with 8 rows will select 8 * (1 - 0.25) = 6 rows.
order_by	<data-masking> Variable or function of variables to order by. To order by multiple variables, wrap them in a data frame or tibble.
with_ties	Should ties be kept together? The default, TRUE, may return more rows than you request. Use FALSE to ignore ties, and return the first n rows.

Examples

library(dplyr, warn.conflicts = FALSE)

dt <- lazy_dt(mtcars)
dt %>% slice(1, 5, 10)
dt %>% slice(-(1:4))

# First and last rows based on existing order
dt %>% slice_head(n = 5)
dt %>% slice_tail(n = 5)

# Rows with minimum and maximum values of a variable
dt %>% slice_min(mpg, n = 5)
dt %>% slice_max(mpg, n = 5)

# slice_min() and slice_max() may return more rows than requested
# in the presence of ties. Use with_ties = FALSE to suppress
dt %>% slice_min(cyl, n = 1)
dt %>% slice_min(cyl, n = 1, with_ties = FALSE)

# slice_sample() allows you to random select with or without replacement
dt %>% slice_sample(n = 5)
dt %>% slice_sample(n = 5, replace = TRUE)

# you can optionally weight by a variable - this code weights by the
# physical weight of the cars, so heavy cars are more likely to get
# selected
dt %>% slice_sample(weight_by = wt, n = 5)

dtplyr documentation built on March 31, 2023, 9:13 p.m.