Convert two numeric ternary outcomes into a factor

## Arguments

- x, y
numeric vectors of -1, 0, and +1 values, indicating down regulation, uncertain response or up-regulation, or numeric vectors that can be converted into such values using a pair of thresholds.

- x_threshold, y_threshold
numeric vector Ranges enclosing the values to be considered uncertain for each of the two vectors..

## Details

This function converts the numerically encoded values into a factor
with the four levels `"xy"`

, `"x"`

, `"y"`

and `"none"`

.
The factor created can be used for faceting or can be mapped to aesthetics.

## Note

This is an utility function that only saves some typing. The same
result can be achieved by a direct call to `factor`

. This
function aims at making it easier to draw quadrant plots with facets
based on the combined outcomes.

## See also

Other Functions for quadrant and volcano plots:
`FC_format()`

,
`outcome2factor()`

,
`scale_colour_outcome()`

,
`scale_shape_outcome()`

,
`scale_y_Pvalue()`

Other scales for omics data:
`outcome2factor()`

,
`scale_colour_logFC()`

,
`scale_shape_outcome()`

,
`scale_x_logFC()`

## Examples

```
xy_outcomes2factor(c(-1, 0, 0, 1, -1), c(0, 1, 0, 1, -1))
#> [1] x y none xy xy
#> Levels: xy x y none
xy_thresholds2factor(c(-1, 0, 0, 1, -1), c(0, 1, 0, 1, -1))
#> [1] x y none xy xy
#> Levels: xy x y none
xy_thresholds2factor(c(-1, 0, 0, 0.1, -5), c(0, 2, 0, 1, -1))
#> [1] x y none xy xy
#> Levels: xy x y none
```