slice: Choose rows by position

In olascodgreat/samife: A Grammar of Data Manipulation

Description

Choose rows by their ordinal position in the tbl. Grouped tbls use the ordinal position within the group.

Usage

slice(.data, ...)

Arguments

.data

A tbl.

...

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. The arguments in ... are automatically quoted and evaluated in the context of the data frame. They support unquoting and splicing. See vignette("programming") for an introduction to these concepts.

Details

Slice does not work with relational databases because they have no intrinsic notion of row order. If you want to perform the equivalent operation, use filter() and row_number().

Tidy data

When applied to a data frame, row names are silently dropped. To preserve, convert to an explicit variable with tibble::rownames_to_column().

See Also

Other single table verbs: arrange, filter, mutate, select, summarise

Examples

slice(mtcars, 1L)
# Similar to tail(mtcars, 1):
slice(mtcars, n())
slice(mtcars, 5:n())
# Rows can be dropped with negative indices:
slice(mtcars, -5:-n())
# In this case, the result will be equivalent to:
slice(mtcars, 1:4)

by_cyl <- group_by(mtcars, cyl)
slice(by_cyl, 1:2)

# Equivalent code using filter that will also work with databases,
# but won't be as fast for in-memory data. For many databases, you'll
# need to supply an explicit variable to use to compute the row number.
filter(mtcars, row_number() == 1L)
filter(mtcars, row_number() == n())
filter(mtcars, between(row_number(), 5, n()))

olascodgreat/samife documentation built on May 13, 2019, 6:11 p.m.