ggperiodic is a simple package that tries to make plotting periodic
data easier. The core idea is that you can specify the *period*
that your data represents and then, at plotting, time, you define the
range that it should be wrapped around. To see it in action, let’s first
create some periodic data with period between 0° and 360°:

```
<- seq(0, 360 - 10, by = 10)*pi/180
x <- seq(-90, 90, by = 10)*pi/180
y
<- expand.grid(x = x, y = y)
Z $z <- with(Z, 1.2*sin(x)*0.4*sin(y*2) -
Z0.5*cos(2*x)*0.5*sin(3*y) +
0.2*sin(4*x)*0.45*cos(2*x))
$x <- Z$x*180/pi
Z$y <- Z$y*180/pi Z
```

Since the vale of `z`

at `x = 0`

and at
`x = 360`

is the same, having both would be redundant and
also create bias when computing statistics because the same point would
be double counted. But when plotting, there’s a problem

```
library(ggplot2)
ggplot(Z) +
geom_contour(aes(x, y, z = z, color = ..level..)) +
coord_polar()
#> Warning: The dot-dot notation (`..level..`) was deprecated in ggplot2 3.4.0.
#> ℹ Please use `after_stat(level)` instead.
#> This warning is displayed once every 8 hours.
#> Call `lifecycle::last_lifecycle_warnings()` to see where this warning was
#> generated.
```

With ggperiodic you can explicitly specify the period that your data represents and then wrap it around any arbitrary range. By printing, you can see the period of each of the periodic variables.

```
library(ggperiodic)
#>
#> Attaching package: 'ggperiodic'
#> The following object is masked from 'package:stats':
#>
#> filter
<- periodic(Z, x = c(0, 360))
Z head(Z)
#> x y z
#> 1 0 -90 -0.25000000
#> 2 10 -90 -0.18056111
#> 3 20 -90 -0.12361453
#> 4 30 -90 -0.08602886
#> 5 40 -90 -0.03806684
#> 6 50 -90 0.04875725
#> x = [0; 360]
```

To manually wrap the data around a range, you can use the same syntax:

```
<- wrap(Z, x = c(-180, 180))
wrapped_z range(wrapped_z$x)
#> [1] -180 180
```

This can be done manually, but ggplot2 will do it automatically, by default wrapping the data around the period.

```
ggplot(Z) +
geom_contour(aes(x, y, z = z, color = ..level..)) +
coord_polar()
```

But it’s easy to change the wrapping range using the same syntax. For example, if we want to see three copies of the data

```
ggplot(Z, x = c(0, 360)*3) +
geom_contour(aes(x, y, z = z, color = ..level..))
```