wl2i {hyperSpec}

Conversion between Wavelength and Spectra Matrix Column Index wl2i returns the column indices for the spectra matrix for the given wavelengths. i2wl converts column indices into wavelengths.

Description

If wavelength is numeric, each of its elements is converted to the respective index. Values outside the range of x@wavelength become NA.

Usage

wl2i(x, wavelength = stop("wavelengths are required."), unlist = TRUE)

i2wl(x, i)

Arguments

x

a hyperSpec object

wavelength

the wavelengths to be converted into column indices, either numeric or a formula, see details.

unlist

if multiple wavelength ranges are given, should the indices be unlisted or kept in a list?

i

the column indices into the spectra matrix for which the wavelength is to be computed

Details

If the range is given as a formula (i.e. start ~ end, a sequence

index corresponding to start : index corresponding to end

is returned. If the wavelengths are not ordered, that may lead to chaos. In this case, call orderwl first.

Two special variables can be used: min and max, corresponding to the lowest and highest wavelength of x, respectively.

start and end may be complex numbers. The resulting index for a complex x is then

index (Re (x)) + Im (x)

Value

A numeric containing the resulting indices for wl2i

i2wl returns a numeric with the wavelengths

Author(s)

C. Beleites

Examples

flu
wl2i (flu, 405 : 407)
wl2i (flu, 405 ~ 407)
  
## beginning of the spectrum to 407 nm 
wl2i (flu, min ~ 407)

## 2 data points from the beginning of the spectrum to 407 nm 
wl2i (flu, min + 2i ~ 407)

## the first 3 data points   
wl2i (flu, min ~ min + 2i)

## from 490 nm to end of the spectrum 
wl2i (flu, 490 ~ max)
  
## the last 8 data points 
wl2i (flu, max - 7i ~ max)
  
## get 450 nm +- 3 data points
wl2i (flu, 450 - 3i ~ 450 + 3i) 
  
wl2i (flu, 300 : 400) ## all NA: 
wl2i (flu, 600 ~ 700) ## NULL: completely outside flu's wavelength range

  
i2wl (chondro, 17:20)