`slidify_vec()`

applies a *summary function* to a rolling sequence of windows.

## Usage

```
slidify_vec(
.x,
.f,
...,
.period = 1,
.align = c("center", "left", "right"),
.partial = FALSE
)
```

## Arguments

- .x
A vector to have a rolling window transformation applied.

- .f
A summary

`[function / formula]`

If a

**function**, e.g.`mean`

, the function is used with any additional arguments,`...`

.If a

**formula**, e.g.`~ mean(., na.rm = TRUE)`

, it is converted to a function.

This syntax allows you to create very compact anonymous functions.

- ...
Additional arguments passed on to the

`.f`

function.- .period
The number of periods to include in the local rolling window. This is effectively the "window size".

- .align
One of "center", "left" or "right".

- .partial
Should the moving window be allowed to return partial (incomplete) windows instead of

`NA`

values. Set to FALSE by default, but can be switched to TRUE to remove`NA`

's.

## Details

The `slidify_vec()`

function is a wrapper for `slider::slide_vec()`

with parameters
simplified "center", "left", "right" alignment.

**Vector Length In == Vector Length Out**

`NA`

values or `.partial`

values
are always returned to ensure the length of the return vector
is the same length of the incoming vector. This ensures easier use with `dplyr::mutate()`

.

**Alignment**

Rolling functions generate `.period - 1`

fewer values than the incoming vector.
Thus, the vector needs to be aligned. Alignment of the vector follows 3 types:

**Center:**`NA`

or`.partial`

values are divided and added to the beginning and end of the series to "Center" the moving average. This is common for de-noising operations. See also`[smooth_vec()]`

for LOESS without NA values.**Left:**`NA`

or`.partial`

values are added to the end to shift the series to the Left.**Right:**`NA`

or`.partial`

values are added to the beginning to shif the series to the Right. This is common in Financial Applications such as moving average cross-overs.

**Partial Values**

The advantage to using

`.partial`

values vs`NA`

padding is that the series can be filled (good for time-series de-noising operations).The downside to partial values is that the partials can become less stable at the regions where incomplete windows are used.

If instability is not desirable for de-noising operations, a suitable alternative
is `smooth_vec()`

, which implements local polynomial regression.

## References

Slider R Package by Davis Vaughan

## See also

Modeling and More Complex Rolling Operations:

`step_slidify()`

- Roll apply for`tidymodels`

modeling`tk_augment_slidify()`

- Add many rolling columns group-wise`slidify()`

- Turn any function into a rolling function. Great for rolling cor, rolling regression, etc.For more complex rolling operations, check out the

`slider`

R package.

Vectorized Transformation Functions:

Box Cox Transformation:

`box_cox_vec()`

Lag Transformation:

`lag_vec()`

Differencing Transformation:

`diff_vec()`

Rolling Window Transformation:

`slidify_vec()`

Loess Smoothing Transformation:

`smooth_vec()`

Fourier Series:

`fourier_vec()`

Missing Value Imputation for Time Series:

`ts_impute_vec()`

## Examples

```
library(tidyverse)
library(tidyquant)
library(timetk)
# Training Data
FB_tbl <- FANG %>%
filter(symbol == "FB") %>%
select(symbol, date, adjusted)
# ---- FUNCTION FORMAT ----
# - The `.f = mean` function is used. Argument `na.rm = TRUE` is passed as ...
FB_tbl %>%
mutate(adjusted_30_ma = slidify_vec(
.x = adjusted,
.period = 30,
.f = mean,
na.rm = TRUE,
.align = "center")) %>%
ggplot(aes(date, adjusted)) +
geom_line() +
geom_line(aes(y = adjusted_30_ma), color = "blue")
#> Warning: Removed 29 row(s) containing missing values (geom_path).
# ---- FORMULA FORMAT ----
# - Anonymous function `.f = ~ mean(., na.rm = TRUE)` is used
FB_tbl %>%
mutate(adjusted_30_ma = slidify_vec(
.x = adjusted,
.period = 30,
.f = ~ mean(., na.rm = TRUE),
.align = "center")) %>%
ggplot(aes(date, adjusted)) +
geom_line() +
geom_line(aes(y = adjusted_30_ma), color = "blue")
#> Warning: Removed 29 row(s) containing missing values (geom_path).
# ---- PARTIAL VALUES ----
# - set `.partial = TRUE`
FB_tbl %>%
mutate(adjusted_30_ma = slidify_vec(
.x = adjusted,
.f = ~ mean(., na.rm = TRUE),
.period = 30,
.align = "center",
.partial = TRUE)) %>%
ggplot(aes(date, adjusted)) +
geom_line() +
geom_line(aes(y = adjusted_30_ma), color = "blue")
# ---- Loess vs Moving Average ----
# - Loess: Using `.degree = 0` to make less flexible. Comperable to a moving average.
FB_tbl %>%
mutate(
adjusted_loess_30 = smooth_vec(adjusted, period = 30, degree = 0),
adjusted_ma_30 = slidify_vec(adjusted, .f = AVERAGE,
.period = 30, .partial = TRUE)
) %>%
ggplot(aes(date, adjusted)) +
geom_line() +
geom_line(aes(y = adjusted_loess_30), color = "red") +
geom_line(aes(y = adjusted_ma_30), color = "blue") +
labs(title = "Loess vs Moving Average")
```