# stack

##### Stack or Unstack Vectors from a Data Frame or List

Stacking vectors concatenates multiple vectors into a single vector along with a factor indicating where each observation originated. Unstacking reverses this operation.

- Keywords
- manip

##### Usage

```
stack(x, …)
# S3 method for default
stack(x, drop=FALSE, …)
# S3 method for data.frame
stack(x, select, drop=FALSE, …)
```unstack(x, …)
# S3 method for default
unstack(x, form, …)
# S3 method for data.frame
unstack(x, form, …)

##### Arguments

- x
a list or data frame to be stacked or unstacked.

- select
an expression, indicating which variable(s) to select from a data frame.

- form
a two-sided formula whose left side evaluates to the vector to be unstacked and whose right side evaluates to the indicator of the groups to create. Defaults to

`formula(x)`

in the data frame method for`unstack`

.- drop
Whether to drop the unused levels from the “ind” column of the return value.

- …
further arguments passed to or from other methods.

##### Details

The `stack`

function is used to transform data available as
separate columns in a data frame or list into a single column that can
be used in an analysis of variance model or other linear model. The
`unstack`

function reverses this operation.

Note that `stack`

applies to *vectors* (as determined by
`is.vector`

): non-vector columns (e.g., factors) will be
ignored with a warning. Where vectors of different types are selected
they are concatenated by `unlist`

whose help page explains
how the type of the result is chosen.

These functions are generic: the supplied methods handle data frames
and objects coercible to lists by `as.list`

.

##### Value

`unstack`

produces a list of columns according to the formula
`form`

. If all the columns have the same length, the resulting
list is coerced to a data frame.

`stack`

produces a data frame with two columns:

the result of concatenating the selected vectors in
`x`

.

a factor indicating from which vector in `x`

the
observation originated.

##### See Also

##### Examples

`library(utils)`

```
require(stats)
formula(PlantGrowth) # check the default formula
pg <- unstack(PlantGrowth) # unstack according to this formula
pg
stack(pg) # now put it back together
stack(pg, select = -ctrl) # omitting one vector
```

*Documentation reproduced from package utils, version 3.4.1, License: Part of R 3.4.1*