R: alr EM-based Imputation for Rounded Zeros

impRZalr {robCompositions} | R Documentation

## alr EM-based Imputation for Rounded Zeros

### Description

A modified EM alr-algorithm for replacing rounded zeros in compositional data sets.

### Usage

    impRZalr(x, pos = ncol(x), dl = rep(0.05, ncol(x) - 1), eps = 1e-04,
      maxit = 50, bruteforce = FALSE, method = "lm", step = FALSE,
      nComp = "boot", R = 10, verbose = FALSE)

### Arguments

`x` | Compositional data
`pos` | Position of the rationing variable for alr transformation
`dl` | Detection limit for each part
`eps` | convergence criteria
`maxit` | maximum number of iterations
`bruteforce` | if TRUE, imputations over dl are set to dl. If FALSE, truncated (Tobit) regression is applied.
`method` | either “lm” (default) or “MM”
`step` | if TRUE, a stepwise (AIC) procedure is applied when fitting models
`nComp` | if determined, it fixes the number of pls components. If “boot”, the number of pls components are estimated using a bootstraped cross validation approach.
`R` | number of bootstrap samples for the determination of pls components. Only important for method “pls”.
`verbose` | additional print output during calculations.

### Details

Statistical analysis of compositional data including zeros runs into problems, because log-ratios cannot be applied. Usually, rounded zeros are considerer as missing not at random missing values. The algorithm first applies an additive log-ratio transformation to the compositions. Then the rounded zeros are imputed using a modified EM algorithm.

### Value

`xOrig` | Original data frame or matrix
`xImp` | Imputed data
`wind` | Index of the missing values in the data
`iter` | Number of iterations
`eps` | eps

### Author(s)

Matthias Templ and Karel Hron

### See Also

`impRZilr`

### Examples

    data(arcticLake)
    x <- arcticLake
    ## generate rounded zeros artificially:
    x[x[,1] < 5, 1] <- 0
    x[x[,2] < 47, 2] <- 0
    xia <- impRZalr(x, pos=3, dl=c(5,47), eps=0.05)
    xia$xImp

[Package robCompositions version 2.0.9 Index]