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Create, modify, and delete columns

Source: R/verb-mutate.R
mutate.tbl_lazy.Rd

These are methods for the dplyr mutate() and transmute() generics. They are translated to computed expressions in the SELECT clause of the SQL query.

Usage

# S3 method for tbl_lazy
mutate(
  .data,
  ...,
  .by = NULL,
  .keep = c("all", "used", "unused", "none"),
  .before = NULL,
  .after = NULL
)

Arguments

.data

A lazy data frame backed by a database query.

...

<data-masking> Variables, or functions of variables. Use desc() to sort a variable in descending order.

.by

[Experimental]

<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.

.keep

Control which columns from .data are retained in the output. Grouping columns and columns created by ... are always kept.

  • "all" retains all columns from .data. This is the default.

  • "used" retains only the columns used in ... to create new columns. This is useful for checking your work, as it displays inputs and outputs side-by-side.

  • "unused" retains only the columns not used in ... to create new columns. This is useful if you generate new columns, but no longer need the columns used to generate them.

  • "none" doesn't retain any extra columns from .data. Only the grouping variables and columns created by ... are kept.

.before, .after

<tidy-select> Optionally, control where new columns should appear (the default is to add to the right hand side). See relocate() for more details.

Value

Another tbl_lazy. Use show_query() to see the generated query, and use collect() to execute the query and return data to R.

Examples

library(dplyr, warn.conflicts = FALSE)

db <- memdb_frame(x = 1:5, y = 5:1)
db %>%
  mutate(a = (x + y) / 2, b = sqrt(x^2L + y^2L)) %>%
  show_query()
#> <SQL>
#> SELECT *, (`x` + `y`) / 2.0 AS `a`, SQRT((POWER(`x`, 2)) + POWER(`y`, 2)) AS `b`
#> FROM `dbplyr_019`

# dbplyr automatically creates subqueries as needed
db %>%
  mutate(x1 = x + 1, x2 = x1 * 2) %>%
  show_query()
#> <SQL>
#> SELECT *, `x1` * 2.0 AS `x2`
#> FROM (
#>   SELECT *, `x` + 1.0 AS `x1`
#>   FROM `dbplyr_019`
#> )