left_join_x: Backfill missing variables via a left join

In xpose.xtras: Extra Functionality for the 'xpose' Package

Backfill missing variables via a left join

Description

<dplyr::left_join> wrapper for xpose_data (and, by inheritance, xp_xtras) objects. Unlike a plain left_join(), a column present in both x and y (other than the join keys) is not duplicated with .x/.y suffixes: missing (NA) values already in x are backfilled from the matching value in y, while non-missing values already in x are left untouched. This makes it straightforward to backfill a variable (or set of variables) that is only partially recorded, from a second data source keyed on the same join variable(s) (e.g. ID).

left_join_x() accepts xpose_data/xp_xtras objects directly, with an additional .problem argument restricting which problem(s) the join is applied to.

left_join() without ⁠_x⁠ is defined as an S3 method on xpose_data, so that the usual <dplyr::left_join> generic dispatches here automatically (xp_xtras objects are handled the same way, via class inheritance).

Usage

left_join_x(
  x,
  y,
  by = NULL,
  copy = FALSE,
  suffix = c(".x", ".y"),
  ...,
  keep = NULL,
  .problem = NULL
)

## S3 method for class 'xpose_data'
left_join(
  x,
  y,
  by = NULL,
  copy = FALSE,
  suffix = c(".x", ".y"),
  ...,
  keep = NULL,
  .problem = NULL
)

Arguments

x	An xpose_data or xp_xtras object.
y	A data frame (or another object coercible to one) to join in.
by	Join specification, as in <dplyr::left_join>. If NULL, a natural join is performed using variables common to x and y.
copy	If x and y are not from the same source and copy = TRUE, y is copied to bring it into the same source as x. See <dplyr::left_join>.
suffix	Suffixes used internally to disambiguate a column shared by x and y before it is backfilled into a single column; not visible in the result.
...	Other parameters passed onto <dplyr::left_join>.
keep	Passed to <dplyr::left_join>. Note that duplicate join key columns (keep = TRUE) are backfilled together like any other shared column, rather than kept separate.
.problem	The problem number(s) to which the join will be applied. Uses all problems if NULL.

Value

An updated xpose_data/xp_xtras object.

Examples

# Some subjects are missing an APGR score in the base dataset
xpdb_missing <- pheno_base %>%
  mutate_x(APGR = dplyr::if_else(ID %in% c("1", "2"), NA, APGR))

# A separate table with the (complete) values, keyed on ID
apgr_lookup <- xpose::get_data(pheno_base, quiet = TRUE) %>%
  dplyr::distinct(ID, APGR)

# Existing APGR values are kept; only the missing ones are filled in
left_join_x(xpdb_missing, apgr_lookup, by = "ID")

xpose.xtras documentation built on Sept. 1, 2026, 5:08 p.m.