`transfo_target.Rd`

This function prepares the encoding of the target variable before running an algorithm using optimal transportation theory.

`transfo_target(z, levels_order = NULL)`

- z
a factor variable (ordered or not). A variable of another type will be, by default, convert to a factor.

- levels_order
a vector corresponding to the values of the levels of z. When the target is ordinal, the levels can be sorted by ascending order. By default, the initial order is remained.

The list returned is:

- NEW
an object of class factor of the same length as z

- LEVELS_NEW
the levels (ordered or not) retained for z

The function `transfo_target`

is an intermediate function direcly implemented in the functions `OT_outcome`

and `OT_joint`

,
two functions dedicated to data fusion (see (1) and (2) for details). Nevertheless, this function can also be used separately to assist user in the conversion
of a target variable (outcome) according to the following rules:

A character variable is converted in factor if the argument

`levels_order`

is set to NULL. In this case, the levels of the factor are assigned by order of appearance in the database.A character variable is converted in ordered factor if the argument

`levels_order`

differs from NULL. In this case, the levels of the factor correspond to those assigned in the argument.A factor stays unchanged if the argument

`levels_order`

is set to NULL. Otherwise the factor is converted in ordered factor and the levels are ordered according to the argument`levels_order`

.A numeric variable, discrete or continuous is converted in factor if the argument

`levels_order`

is set to NULL, and the related levels are the values assigned in ascending order.A numeric variable, discrete or continuous is converted in ordered factor if the argument

`levels_order`

differed from NULL, and the related levels correspond to those assigned in the argument.

Gares V, Dimeglio C, Guernec G, Fantin F, Lepage B, Korosok MR, savy N (2019). On the use of optimal transportation theory to recode variables and application to database merging. The International Journal of Biostatistics. Volume 16, Issue 1, 20180106, eISSN 1557-4679. doi:10.1515/ijb-2018-0106

Gares V, Omer J (2020) Regularized optimal transport of covariates and outcomes in data recoding. Journal of the American Statistical Association. doi:10.1080/01621459.2020.1775615

```
y <- rnorm(100, 30, 10)
ynew1 <- transfo_target(y)
#> Your target y was numeric ... By default, it has been converted in factor of integers
#> 39 remaining levels
newlev <- unique(as.integer(y))
ynew2 <- transfo_target(y, levels_order = newlev)
#> Your target y was numeric ... By default, it has been converted in factor of integers
newlev2 <- newlev[-1]
ynew3 <- transfo_target(y, levels_order = newlev2)
#> Your target y was numeric ... By default, it has been converted in factor of integers
#> Inappropriate number or declared labels of levels
#> The default labels have been kept
outco <- c(rep("A", 25), rep("B", 50), rep("C", 25))
outco_new1 <- transfo_target(outco, levels_order = c("B", "C", "A"))
outco_new2 <- transfo_target(outco, levels_order = c("E", "C", "A", "F"))
#> Inappropriate number or declared labels of levels
#> The default levels have been kept
outco_new3 <- transfo_target(outco)
outco2 <- c(rep("A", 25), NA, rep("B", 50), rep("C", 25), NA, NA)
gg <- transfo_target(outco2)
hh <- transfo_target(outco2, levels_order = c("B", "C", "A"))
```