Multi-Step Adaptive Elastic-Net

## Usage

```
msaenet(
x,
y,
family = c("gaussian", "binomial", "poisson", "cox"),
init = c("enet", "ridge"),
alphas = seq(0.05, 0.95, 0.05),
tune = c("cv", "ebic", "bic", "aic"),
nfolds = 5L,
rule = c("lambda.min", "lambda.1se"),
ebic.gamma = 1,
nsteps = 2L,
tune.nsteps = c("max", "ebic", "bic", "aic"),
ebic.gamma.nsteps = 1,
scale = 1,
lower.limits = -Inf,
upper.limits = Inf,
penalty.factor.init = rep(1, ncol(x)),
seed = 1001,
parallel = FALSE,
verbose = FALSE
)
```

## Arguments

- x
Data matrix.

- y
Response vector if

`family`

is`"gaussian"`

,`"binomial"`

, or`"poisson"`

. If`family`

is`"cox"`

, a response matrix created by`Surv`

.- family
Model family, can be

`"gaussian"`

,`"binomial"`

,`"poisson"`

, or`"cox"`

.- init
Type of the penalty used in the initial estimation step. Can be

`"enet"`

or`"ridge"`

. See`glmnet`

for details.- alphas
Vector of candidate

`alpha`

s to use in`cv.glmnet`

.- tune
Parameter tuning method for each estimation step. Possible options are

`"cv"`

,`"ebic"`

,`"bic"`

, and`"aic"`

. Default is`"cv"`

.- nfolds
Fold numbers of cross-validation when

`tune = "cv"`

.- rule
Lambda selection criterion when

`tune = "cv"`

, can be`"lambda.min"`

or`"lambda.1se"`

. See`cv.glmnet`

for details.- ebic.gamma
Parameter for Extended BIC penalizing size of the model space when

`tune = "ebic"`

, default is`1`

. For details, see Chen and Chen (2008).- nsteps
Maximum number of adaptive estimation steps. At least

`2`

, assuming adaptive elastic-net has only one adaptive estimation step.- tune.nsteps
Optimal step number selection method (aggregate the optimal model from the each step and compare). Options include

`"max"`

(select the final-step model directly), or compare these models using`"ebic"`

,`"bic"`

, or`"aic"`

. Default is`"max"`

.- ebic.gamma.nsteps
Parameter for Extended BIC penalizing size of the model space when

`tune.nsteps = "ebic"`

, default is`1`

.- scale
Scaling factor for adaptive weights:

`weights = coefficients^(-scale)`

.- lower.limits
Lower limits for coefficients. Default is

`-Inf`

. For details, see`glmnet`

.- upper.limits
Upper limits for coefficients. Default is

`Inf`

. For details, see`glmnet`

.- penalty.factor.init
The multiplicative factor for the penalty applied to each coefficient in the initial estimation step. This is useful for incorporating prior information about variable weights, for example, emphasizing specific clinical variables. To make certain variables more likely to be selected, assign a smaller value. Default is

`rep(1, ncol(x))`

.- seed
Random seed for cross-validation fold division.

- parallel
Logical. Enable parallel parameter tuning or not, default is

`FALSE`

. To enable parallel tuning, load the`doParallel`

package and run`registerDoParallel()`

with the number of CPU cores before calling this function.- verbose
Should we print out the estimation progress?

## References

Nan Xiao and Qing-Song Xu. (2015). Multi-step adaptive elastic-net:
reducing false positives in high-dimensional variable selection.
*Journal of Statistical Computation and Simulation* 85(18), 3755--3765.

## Author

Nan Xiao <https://nanx.me>

## Examples

```
dat <- msaenet.sim.gaussian(
n = 150, p = 500, rho = 0.6,
coef = rep(1, 5), snr = 2, p.train = 0.7,
seed = 1001
)
msaenet.fit <- msaenet(
dat$x.tr, dat$y.tr,
alphas = seq(0.2, 0.8, 0.2),
nsteps = 3L, seed = 1003
)
print(msaenet.fit)
#> Call: msaenet(x = dat$x.tr, y = dat$y.tr, alphas = seq(0.2, 0.8, 0.2),
#> nsteps = 3L, seed = 1003)
#> Df %Dev Lambda
#> 1 8 0.797121 1.219202e+15
msaenet.nzv(msaenet.fit)
#> [1] 2 4 5 35 114 269 363 379
msaenet.fp(msaenet.fit, 1:5)
#> [1] 5
msaenet.tp(msaenet.fit, 1:5)
#> [1] 3
msaenet.pred <- predict(msaenet.fit, dat$x.te)
msaenet.rmse(dat$y.te, msaenet.pred)
#> [1] 2.839212
plot(msaenet.fit)
```