medpolish {eda}R Documentation

Median Polish of a Matrix


Fits an additive model using Tukey's median polish procedure.


medpolish(x, eps = 0.01, maxiter = 10, trace.iter = TRUE,
          na.rm = FALSE)


x a numeric matrix.
eps real number greater than 0. A tolerance for convergence: see Details.
maxiter the maximum number of iterations
trace.iter logical. Should progress in convergence be reported?
na.rm logical. Should missing values be removed?


The model fitted is additive (constant + rows + columns). The algorithm works by alternately removing the row and column medians, and continues until the proportional reduction in the sum of absolute residuals is less than eps or until there have been maxiter iterations. The sum of absolute residuals is printed at each iteration of the fitting process, if trace.iter is TRUE. If na.rm is FALSE the presence of any NA value in x will cause an error, otherwise NA values are ignored.

medpolish returns an object of class medpolish (see below). There are printing and plotting methods for this class, which are invoked via by the generics print and plot.


An object of class medpolish with the following named components:

overall the fitted constant term.
row the fitted row effects.
col the fitted column effects.
residuals the residuals.
name the name of the dataset.


Tukey, J. W. (1977). Exploratory Data Analysis, Reading Massachusetts: Addison-Wesley.

See Also

median; aov for a mean instead of median decomposition.


## Deaths from sport parachuting;  from ABC of EDA, p.224:
deaths <-
          c( 7, 4, 7),
          c( 8, 2,10),
          c(15, 9,10),
          c( 0, 2, 0))
dimnames(deaths) <- list(c("1-24", "25-74", "75-199", "200++", "NA"),
(med.d <- medpolish(deaths))
## Check decomposition:
all(deaths == med.d$overall + outer(med.d$row,med.d$col, "+") + med.d$resid)

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