pack: Pack and unpack

In tidyverse/tidyr: Tidy Messy Data

Pack and unpack

Description

Packing and unpacking preserve the length of a data frame, changing its width. pack() makes df narrow by collapsing a set of columns into a single df-column. unpack() makes data wider by expanding df-columns back out into individual columns.

Usage

pack(.data, ..., .names_sep = NULL, .error_call = current_env())

unpack(
  data,
  cols,
  ...,
  names_sep = NULL,
  names_repair = "check_unique",
  error_call = current_env()
)

Arguments

...	For pack(), <tidy-select> columns to pack, specified using name-variable pairs of the form new_col = c(col1, col2, col3). The right hand side can be any valid tidy select expression. For unpack(), these dots are for future extensions and must be empty.
data, .data	A data frame.
cols	<tidy-select> Columns to unpack.
names_sep, .names_sep	If NULL, the default, the names will be left as is. In pack(), inner names will come from the former outer names; in unpack(), the new outer names will come from the inner names. If a string, the inner and outer names will be used together. In unpack(), the names of the new outer columns will be formed by pasting together the outer and the inner column names, separated by names_sep. In pack(), the new inner names will have the outer names + names_sep automatically stripped. This makes names_sep roughly symmetric between packing and unpacking.
names_repair	Used to check that output data frame has valid names. Must be one of the following options: ⁠"minimal⁠": no name repair or checks, beyond basic existence, ⁠"unique⁠": make sure names are unique and not empty, ⁠"check_unique⁠": (the default), no name repair, but check they are unique, ⁠"universal⁠": make the names unique and syntactic a function: apply custom name repair. tidyr_legacy: use the name repair from tidyr 0.8. a formula: a purrr-style anonymous function (see rlang::as_function()) See vctrs::vec_as_names() for more details on these terms and the strategies used to enforce them.
error_call, .error_call	The execution environment of a currently running function, e.g. caller_env(). The function will be mentioned in error messages as the source of the error. See the call argument of abort() for more information.

Details

Generally, unpacking is more useful than packing because it simplifies a complex data structure. Currently, few functions work with df-cols, and they are mostly a curiosity, but seem worth exploring further because they mimic the nested column headers that are so popular in Excel.

Examples

# Packing -------------------------------------------------------------------
# It's not currently clear why you would ever want to pack columns
# since few functions work with this sort of data.
df <- tibble(x1 = 1:3, x2 = 4:6, x3 = 7:9, y = 1:3)
df
df %>% pack(x = starts_with("x"))
df %>% pack(x = c(x1, x2, x3), y = y)

# .names_sep allows you to strip off common prefixes; this
# acts as a natural inverse to name_sep in unpack()
iris %>%
  as_tibble() %>%
  pack(
    Sepal = starts_with("Sepal"),
    Petal = starts_with("Petal"),
    .names_sep = "."
  )

# Unpacking -----------------------------------------------------------------
df <- tibble(
  x = 1:3,
  y = tibble(a = 1:3, b = 3:1),
  z = tibble(X = c("a", "b", "c"), Y = runif(3), Z = c(TRUE, FALSE, NA))
)
df
df %>% unpack(y)
df %>% unpack(c(y, z))
df %>% unpack(c(y, z), names_sep = "_")

tidyverse/tidyr documentation built on Oct. 30, 2024, 1:53 a.m.