# optimized.sample.variance: Optimized sample variance In jeffreyevans/spatialEco: Spatial Analysis and Modelling Utilities (development version)

## Description

Draws an optimal sample that minimizes or maximizes the sample variance

## Usage

 `1` ```optimized.sample.variance(x, n, type = "maximized") ```

## Arguments

 `x` A vector to draw a sample from `n` Number of samples to draw `type` Type of sample variance optimization c("maximized", "minimized")

## Value

A data.frame with "idx" representing the index of the original vector and "y" is the value of the sampled data

## Author(s)

Jeffrey S. Evans <[email protected]>

## Examples

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42``` ``` library(sp) data(meuse) coordinates(meuse) <- ~x+y n = 15 # Draw n samples that maximize the variance of y ( max.sv <- optimized.sample.variance(meuse\$zinc, 15) ) # Draw n samples that minimize the variance of y ( min.sv <- optimized.sample.variance(meuse\$zinc, 15, type="minimized") ) # Plot results plot(meuse, pch=19, col="grey") plot(meuse[max.sv\$idx,], col="red", add=TRUE, pch=19) plot(meuse[min.sv\$idx,], col="blue", add=TRUE, pch=19) box() legend("topleft", legend=c("population","maximized variance", "minimized variance"), col=c("grey","red","blue"), pch=c(19,19,19)) ## Not run: # Raster example (not memory safe) library(raster) r <- raster(system.file("external/test.grd", package="raster")) # Calculate optimal sample variance and coerce to SpatialPointDataFrame using xyFromCell ( min.sv <- optimized.sample.variance(getValues(r), n, type="minimized") ) min.sv <- sp::SpatialPointsDataFrame(xyFromCell(r, min.sv[,"idx"], spatial=TRUE), data=min.sv) ( max.sv <- optimized.sample.variance(getValues(r), n) ) max.sv <- sp::SpatialPointsDataFrame(xyFromCell(r, max.sv[,"idx"], spatial=TRUE), data=max.sv) plot(r) plot(max.sv, col="blue", add=TRUE, pch=19) plot(min.sv, col="red", add=TRUE, pch=19) box() legend("topleft", legend=c("maximized variance", "minimized variance"), col=c("red","blue"), pch=c(19,19)) ## End(Not run) ```

jeffreyevans/spatialEco documentation built on Nov. 10, 2018, 4:13 a.m.