# centr: Centers of classes In mlesnoff/rnirs: Dimension reduction, Regression and Discrimination for Chemometrics

 centr R Documentation

## Centers of classes

### Description

Calculation of the centers (eg. mean or median) of classes of row observations of a data set.

### Usage

``centr(X, Y = NULL, FUN = mean, ...)``

### Arguments

 `X` A `n x p` matrix or data frame (usually spectra) on which are calculated the centers. `Y` A vector of length `n` defining the class membership of the row observations. Default to `NULL` (all the rows of are considered). `FUN` The function used in the aggregation (Default to mean). `...` Optionnal arguments to pass in the function defined in `FUN`.

### Details

`centr` uses function `aggregate`.

### Value

A list of outputs.

### Examples

``````
n <- 8
p <- 6
set.seed(1)
X <- matrix(rnorm(n * p, mean = 10), ncol = p, byrow = TRUE)
y <- sample(1:2, size = n, replace = TRUE)
set.seed(NULL)

centr(X, y)
centr(X, y, FUN = median)

data(datforages)

Xr <- datforages\$Xr
yr <- datforages\$yr
table(yr)

u <- centr(Xr, yr)\$centers
v <- centr(Xr, yr, FUN = median)\$centers

oldpar <- par(mfrow = c(1, 1))
par(mfrow = c(1, 2))
plotsp(u, col = 1:4, main = "Mean")
plotsp(v, col = 1:4, main = "Median")
par(oldpar)

x <- Xr[1:20, ]
plotsp(x, ylab = "Absorbance", col = "grey")
u <- centr(x)\$centers
plotsp(u, col = "red", add = TRUE, lwd = 2)

``````

mlesnoff/rnirs documentation built on April 24, 2023, 4:17 a.m.