robCompositions (version 1.6.3)

impCoda: Imputation of missing values in compositional data

Description

This function offers different methods for the imputation of missing values in compositional data. Missing values are initialized with proper values. Then iterative algorithms try to find better estimations for the former missing values.

Usage

impCoda(x, maxit = 10, eps = 0.5, method = "ltsReg", closed = FALSE, init = "KNN", k = 5, dl = rep(0.05, ncol(x)), noise=0.1, bruteforce=FALSE)

Arguments

x

data frame or matrix

maxit

maximum number of iterations

eps

convergence criteria

method

imputation method

closed

imputation of transformed data (using ilr transformation) or in the original space (closed equals TRUE)

init

method for initializing missing values

k

number of nearest neighbors (if init $==$ KNN)

dl

detection limit(s), only important for the imputation of rounded zeros

noise

amount of adding random noise to predictors after convergency

bruteforce

if TRUE, imputations over dl are set to dl. If FALSE, truncated (Tobit) regression is applied.

Value

• xOrig
  Original data frame or matrix
• xImp
  Imputed data
• criteria
  Sum of the Aitchison distances from the present and previous iteration
• iter
  Number of iterations
• maxit
  Maximum number of iterations
• w
  Amount of imputed values
• wind
  Index of the missing values in the data

Details

eps: The algorithm is finished as soon as the imputed values stabilize, i.e. until the sum of Aitchison distances from the present and previous iteration changes only marginally (eps).\ method: Several different methods can be chosen, such as ltsReg: least trimmed squares regression is used within the iterative procedure. lm: least squares regression is used within the iterative procedure. classical: principal component analysis is used within the iterative procedure. ltsReg2: least trimmed squares regression is used within the iterative procedure. The imputated values are perturbed in the direction of the predictor by values drawn form a normal distribution with mean and standard deviation related to the corresponding residuals and multiplied by noise. method roundedZero is experimental. It imputes rounded zeros within our iterative framework.

References

Hron, K. and Templ, M. and Filzmoser, P. (2010) Imputation of missing values for compositional data using classical and robust methods Computational Statistics and Data Analysis, vol 54 (12), pages 3095-3107.

See Also

impKNNa, isomLR

Examples

data(expenditures)
x <- expenditures
x[1,3]
x[1,3] <- NA
xi <- impCoda(x)$xImp
xi[1,3]
s1 <- sum(x[1,-3])
impS <- sum(xi[1,-3])
xi[,3] * s1/impS