# Sparse partial robust M regression

### Description

Sparse partial robust M regression for models with univariate response. This method for dimension reduction and regression analysis yields estimates with a partial least squares alike interpretability that are both sparse and robust to both vertical outliers and leverage points. The sparsity is tuned with an L1 penalty.

### Usage

1 2 3 |

### Arguments

`formula` |
an object of class formula. |

`data` |
a data frame which contains the variables given in formula or a list of two elements, where the first element is the response vector and the second element is a matrix of the explanatory variables. |

`a` |
the number of SPRMS components to be estimated in the model. |

`eta` |
a tuning parameter for the sparsity with 0\le eta<1. |

`fun` |
an internal weighting function for case weights. Choices are |

`probp1` |
the 1-alpha value at which to set the first outlier cutoff for the weighting function. |

`hampelp2` |
the 1-alpha values for second cutoff. Only applies to |

`hampelp3` |
the 1-alpha values for third cutoff. Only applies to |

`center` |
type of centering of the data in form of a string that matches an R function, e.g. |

`scale` |
type of scaling for the data in form of a string that matches an R function, e.g. |

`print` |
logical, default is |

`numit` |
the maximum number of iterations for the convergence of the coefficient estimates. |

`prec` |
a value for the precision of estimation of the coefficients. |

### Details

The NIPLS algorithm with a L1 sparsity constrained combined with weighted regression is used for the model estimation.

`a`

is the number of components in the model. Note that it is not possible to simply reduce the number of weighting vectors to obtain a model with a smaller number of components. Each model has to be estimated separately due to its dependence on robust case weights.

### Value

sprms returns an object of class sprm.

Functions `summary`

, `predict`

and `plot`

are available. Also the generic functions `coefficients`

, `fitted.values`

and `residuals`

can be used to extract the corresponding elements from the sprm object.

`coefficients` |
vector of coefficients of the weighted regression model. |

`intercept` |
intercept of weighted regression model. |

`wy` |
the case weights in the y space. |

`wt` |
the case weights in the score space. |

`w` |
the overall case weights used for weighted regression (depending on the weight function). |

`scores` |
the matrix of scores. |

`R` |
Direction vectors (or weighting vectors or rotation matrix) to obtain the scores. |

`loadings` |
the matrix of loadings. |

`fitted.values` |
the vector of estimated response values. |

`residuals` |
vector of residuals, true response minus estimated response. |

`coefficients.scaled` |
vector of coefficients of the weighted regression model with scaled data. |

`intercept.scaled` |
intercept of weighted regression model with scaled data. |

`YMeans` |
value used internally to center response. |

`XMean` |
vector used internally to center data. |

`Xscales` |
vector used internally to scale data. |

`Yscales` |
value used internally to scale response. |

`Yvar` |
percentage of contribution for each component to the explanation of the variance of the response. |

`Xvar` |
percentage of contribution for each component to the explanation of the variance of the variables. |

`inputs` |
list of inputs: parameters, data and scaled data. |

`used.vars` |
Indices of variables included in the model. |

### Author(s)

Sven Serneels, BASF Corp and Irene Hoffmann

### References

Hoffmann, I., Serneels, S., Filzmoser, P., Croux, C. (2015). Sparse partial robust M regression. Chemometrics and Intelligent Laboratory Systems, 149, 50-59.

Serneels, S., Croux, C., Filzmoser, P., Van Espen, P.J. (2005). Partial Robust M-Regression. Chemometrics and Intelligent Laboratory Systems, 79, 55-64.

### See Also

`sprmsCV`

, `plot.sprm`

, `biplot.sprm`

, `predict.sprm`

, `prms`

### Examples

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | ```
set.seed(50235)
U1 <- c(rep(3,20), rep(4,30))
U2 <- rep(3.5,50)
X1 <- replicate(5, U1+rnorm(50))
X2 <- replicate(20, U2+rnorm(50))
X <- cbind(X1,X2)
beta <- c(rep(1, 5), rep(0,20))
e <- c(rnorm(45,0,1.5),rnorm(5,-20,1))
y <- X%*%beta + e
d <- as.data.frame(X)
d$y <- y
mod <- sprms(y~., data=d, a=1, eta=0.5, fun="Hampel")
sprmfit <- predict(mod)
plot(y,sprmfit, main="SPRM")
abline(0,1)
``` |

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