The tsibble package is
where the name `slide()`

originated. It contained original
implementations of `slide()`

and friends, along with
variations like `tile()`

and `stretch()`

, all of
which have been superceded by slider. As of tsibble 1.0.0, those
functions have been completely removed in favor of using slider. The
goal of this vignette is to explain how to transition from tsibble to
slider.

tsibble’s `.size`

and `.align`

arguments are
roughly equivalent to using `.before`

and `.after`

in slider. In tsibble, you’d specify the full width of the window with
`.size`

, and then you’d specify how to construct that window
by `.align`

ing yourself to the left, right, or center. In
slider, you always start at the “current” element, and then specify how
many elements `.before`

and `.after`

the current
element that you want in the window. The width of the window in slider
terms could be computed as `.after - .before + 1`

.

```
<- 1:3
x
# The current element, and 1 before it
::slide(x, identity, .before = 1, .complete = TRUE)
slider#> [[1]]
#> NULL
#>
#> [[2]]
#> [1] 1 2
#>
#> [[3]]
#> [1] 2 3
```

```
# Window size of 2, assume the current element is the right side of the window
::slide(x, identity, .size = 2, .align = "right")
tsibble#> [[1]]
#> [1] NA
#>
#> [[2]]
#> [1] 1 2
#>
#> [[3]]
#> [1] 2 3
```

We also have to set the `.complete`

argument of slider’s
`slide()`

to `TRUE`

, as by default slider allows
partial windows, but tsibble’s version does not. The equivalent argument
to this in tsibble is `.partial`

(note that they are
interpreted inversely of each other).

There is no `.fill`

equivalent in slider. slider always
uses the vctrs definition of a missing value (a typed `NA`

for most vectors, a `NULL`

for lists). This is why the slider
result above has a `NULL`

, while the tsibble result used an
`NA`

(the default `.fill`

value in tsibble).

Specifying windows using `.before`

and `.after`

might first feel a bit unnatural to a tsibble or zoo user, but it is
generally more flexible. You can generate irregular windows that aren’t
possible with tsibble, like:

```
# The current element, along with 1 before and 3 after (if they exist)
::slide(1:6, identity, .before = 1, .after = 3)
slider#> [[1]]
#> [1] 1 2 3 4
#>
#> [[2]]
#> [1] 1 2 3 4 5
#>
#> [[3]]
#> [1] 2 3 4 5 6
#>
#> [[4]]
#> [1] 3 4 5 6
#>
#> [[5]]
#> [1] 4 5 6
#>
#> [[6]]
#> [1] 5 6
```

As you will see in the next section, expanding windows are easy to
create by setting `.before`

or `.after`

to
`Inf`

.

This syntax also translates naturally to `slide_index()`

,
where the bounds of the window are (by default) computed as
`.i - .before`

and `.i + .after`

, which often
cannot be expressed by a single window size value.

Tiling uses non-overlapping windows. For example, this segments
`x`

into 4 non-overlapping buckets, where as many buckets as
possible have a window size of 3.

```
<- 1:10
x
::tile(x, identity, .size = 3)
tsibble#> [[1]]
#> [1] 1 2 3
#>
#> [[2]]
#> [1] 4 5 6
#>
#> [[3]]
#> [1] 7 8 9
#>
#> [[4]]
#> [1] 10
```

There is no direct equivalent to this in slider, but you can get
close with `slide()`

. `tile()`

seems to left-align
the index, so we need the current element plus two `.after`

it. Since this is a non-overlapping window, we want to
`.step`

forward by the size of the window, three.

```
<- slider::slide(x, identity, .after = 2, .step = 3)
result
result#> [[1]]
#> [1] 1 2 3
#>
#> [[2]]
#> NULL
#>
#> [[3]]
#> NULL
#>
#> [[4]]
#> [1] 4 5 6
#>
#> [[5]]
#> NULL
#>
#> [[6]]
#> NULL
#>
#> [[7]]
#> [1] 7 8 9
#>
#> [[8]]
#> NULL
#>
#> [[9]]
#> NULL
#>
#> [[10]]
#> [1] 10
```

This isn’t exactly the same, as `slide()`

is guaranteed to
be size-stable, returning an object with the same size as
`.x`

. However, if you `purrr::compact()`

the
result to drop the `NULL`

values, then they are
equivalent.

```
::compact(result)
purrr#> [[1]]
#> [1] 1 2 3
#>
#> [[2]]
#> [1] 4 5 6
#>
#> [[3]]
#> [1] 7 8 9
#>
#> [[4]]
#> [1] 10
```

To construct expanding windows with tsibble, you’ve probably used
`stretch()`

. This fixes an initial window size, and then
expands to add more observations without dropping any.

```
<- 1:4
x
::stretch(x, identity)
tsibble#> [[1]]
#> [1] 1
#>
#> [[2]]
#> [1] 1 2
#>
#> [[3]]
#> [1] 1 2 3
#>
#> [[4]]
#> [1] 1 2 3 4
```

With slider, you can set `.before = Inf`

to select the
current element plus all elements before this one.

```
::slide(x, identity, .before = Inf)
slider#> [[1]]
#> [1] 1
#>
#> [[2]]
#> [1] 1 2
#>
#> [[3]]
#> [1] 1 2 3
#>
#> [[4]]
#> [1] 1 2 3 4
```

`stretch()`

allows you to set `.init`

to fix an
initial minimum window size:

```
::stretch(x, identity, .init = 3)
tsibble#> [[1]]
#> [1] NA
#>
#> [[2]]
#> [1] NA
#>
#> [[3]]
#> [1] 1 2 3
#>
#> [[4]]
#> [1] 1 2 3 4
```

There isn’t a direct equivalent of this in slider, but your function
could return `NULL`

if the current window size didn’t hold
enough elements:

```
<- function(x) {
identity3 if (length(x) < 3) {
NULL
else {
}
x
}
}
::slide(x, identity3, .before = Inf)
slider#> [[1]]
#> NULL
#>
#> [[2]]
#> NULL
#>
#> [[3]]
#> [1] 1 2 3
#>
#> [[4]]
#> [1] 1 2 3 4
```