nest: Nest and unnest

In tidyfst: Tidy Verbs for Fast Data Manipulation

Nest and unnest

Description

Create or melt list columns in data.frame.

Analogous function for nest and unnest in tidyr. unnest_dt will automatically remove other list-columns except for the target list-columns (which would be unnested later). Also, squeeze_dt is designed to merge multiple columns into list column.

Usage

nest_dt(.data, ..., mcols = NULL, .name = "ndt")

unnest_dt(.data, ...)

squeeze_dt(.data, ..., .name = "ndt")

chop_dt(.data, ...)

unchop_dt(.data, ...)

Arguments

.data	data.table, nested or unnested
...	The variables for nest group(for nest_dt), columns to be nested(for squeeze_dt and chop_dt), or column(s) to be unnested(for unnest_dt). Could recieve anything that select_dt could receive.
mcols	Name-variable pairs in the list, form like
.name	Character. The nested column name. Defaults to "ndt". list(petal="^Pe",sepal="^Se"), see example.

Details

In the nest_dt, the data would be nested to a column named 'ndt', which is short for nested data.table.

The squeeze_dt would not remove the originial columns.

The unchop_dt is the reverse operation of chop_dt.

These functions are experiencing the experimental stage, especially the unnest_dt. If they don't work on some circumtances, try tidyr package.

Value

data.table, nested or unnested

References

https://www.r-bloggers.com/much-faster-unnesting-with-data-table/

https://stackoverflow.com/questions/25430986/create-nested-data-tables-by-collapsing-rows-into-new-data-tables

See Also

nest, chop

Examples

# examples for nest_dt
# nest by which columns?
 mtcars %>% nest_dt(cyl)
 mtcars %>% nest_dt("cyl")
 mtcars %>% nest_dt(cyl,vs)
 mtcars %>% nest_dt(vs:am)
 mtcars %>% nest_dt("cyl|vs")
 mtcars %>% nest_dt(c("cyl","vs"))

 # change the nested column name
 mtcars %>% nest_dt(cyl,.name = "data")

# nest two columns directly
iris %>% nest_dt(mcols = list(petal="^Pe",sepal="^Se"))

# nest more flexibly
iris %>% nest_dt(mcols = list(ndt1 = 1:3,
  ndt2 = "Pe",
  ndt3 = Sepal.Length:Sepal.Width))

# examples for unnest_dt
# unnest which column?
 mtcars %>% nest_dt("cyl|vs") %>%
   unnest_dt(ndt)
 mtcars %>% nest_dt("cyl|vs") %>%
   unnest_dt("ndt")

df <- data.table(
  a = list(c("a", "b"), "c"),
  b = list(c(TRUE,TRUE),FALSE),
  c = list(3,c(1,2)),
  d = c(11, 22)
)

df
df %>% unnest_dt(a)
df %>% unnest_dt(2)
df %>% unnest_dt("c")
df %>% unnest_dt(cols = names(df)[3])

# You can unnest multiple columns simultaneously
df %>% unnest_dt(1:3)
df %>% unnest_dt(a,b,c)
df %>% unnest_dt("a|b|c")

# examples for squeeze_dt
# nest which columns?
iris %>% squeeze_dt(1:2)
iris %>% squeeze_dt("Se")
iris %>% squeeze_dt(Sepal.Length:Petal.Width)
iris %>% squeeze_dt(1:2,.name = "data")

# examples for chop_dt
df <- data.table(x = c(1, 1, 1, 2, 2, 3), y = 1:6, z = 6:1)
df %>% chop_dt(y,z)
df %>% chop_dt(y,z) %>% unchop_dt(y,z)

tidyfst documentation built on Sept. 16, 2024, 9:06 a.m.