Fixing an initial window and expanding more observations:

`stretch()`

always returns a list.

`stretch_lgl()`

, `stretch_int()`

, `stretch_dbl()`

, `stretch_chr()`

use the same
arguments as `stretch()`

, but return vectors of the corresponding type.

`stretch_dfr()`

`stretch_dfc()`

return data frames using row-binding & column-binding.

stretch(.x, .f, ..., .size = 1, .init = 1)
stretch_dfr(.x, .f, ..., .size = 1, .init = 1, .id = NULL)
stretch_dfc(.x, .f, ..., .size = 1, .init = 1)

## Arguments

.x |
An object to slide over. |

.f |
A function, formula, or atomic vector.
If a **function**, it is used as is.
If a **formula**, e.g. `~ .x + 2` , it is converted to a function. There
are three ways to refer to the arguments:
For a single argument function, use `.`
For a two argument function, use `.x` and `.y`
For more arguments, use `..1` , `..2` , `..3` etc
This syntax allows you to create very compact anonymous functions.
If **character vector**, **numeric vector**, or **list**, it
is converted to an extractor function. Character vectors index by name
and numeric vectors index by position; use a list to index by position
and name at different levels. Within a list, wrap strings in `get-attr()`
to extract named attributes. If a component is not present, the value of
`.default` will be returned. |

... |
Additional arguments passed on to `.f` . |

.size |
An integer for window size. If positive, moving forward from left
to right; if negative, moving backward (from right to left). |

.init |
A positive integer for an initial window size. |

.id |
If not `NULL` a variable with this name will be created
giving either the name or the index of the data frame. |

## See also

## Examples

.x <- 1:5
.lst <- list(x = .x, y = 6:10, z = 11:15)
stretch_dbl(.x, mean, .size = 2)

#> [1] 1 2 3

stretch_lgl(.x, ~ mean(.) > 2, .size = 2)

#> [1] FALSE FALSE TRUE

stretch(.lst, ~ ., .size = 2)

#> [[1]]
#> [[1]]$x
#> [1] 1 2 3 4 5
#>
#>
#> [[2]]
#> [[2]]$x
#> [1] 1 2 3 4 5
#>
#> [[2]]$y
#> [1] 6 7 8 9 10
#>
#> [[2]]$z
#> [1] 11 12 13 14 15
#>
#>