Compute and plot various measures of central tendency and
spread for a `Spectra`

object. Several different measures/spreads
are available. These are useful as an overview of where a data set varies
the most.

```
surveySpectra(
spectra,
method = c("sd", "sem", "sem95", "mad", "iqr"),
by.gr = TRUE,
...
)
surveySpectra2(
spectra,
method = c("sd", "sem", "sem95", "mad", "iqr"),
lab.pos = 0.9 * max(spectra$freq),
...
)
```

## Arguments

- spectra
An object of S3 class `Spectra()`

.

- method
Character. One of ```
c("sd", "sem", "sem95", "mad",
"iqr")
```

.

- by.gr
Logical, indicating if the analysis is to be done by group or
not. Applies to `surveySpectra`

only.

- ...
Parameters to be passed to the plotting routines. *Applies to base graphics only*.

- lab.pos
Numeric, giving the frequency where the label should be drawn.
Applies to `surveySpectra2`

only.

## Value

The returned value depends on the graphics option selected (see `GraphicsOptions()`

).

`base`

: None. Side effect is a plot.

`ggplot2`

: The plot is displayed, and a `ggplot2`

object is returned if the value is assigned. The plot can be modified in the usual `ggplot2`

manner.

## Details

For `surveySpectra`

the method choice works as follows: `sd`

plots
the mean spectrum +/- the standard deviation, `sem`

plots the mean
spectrum +/- the standard error of the mean, `sem95`

plots the mean
spectrum +/- the standard error at the 95 percent confidence interval,
`mad`

plots the median spectrum +/- the median absolute deviation, and
finally, `iqr`

plots the median spectrum + the upper hinge and - the
lower hinge.

For `surveySpectra2`

, the spectra are mean centered and plotted. Below
that, the relative summary statistic is plotted, offset, but on the same
scale.

## Functions

`surveySpectra()`

: Spectral survey emphasizing mean or median spectrum, optionally by group.

`surveySpectra2()`

: Spectral survey emphasizing variation among spectra.

## Author

Bryan A. Hanson (DePauw University), Tejasvi Gupta.

## Examples

```
# This example assumes the graphics output is set to ggplot2 (see ?GraphicsOptions).
library("ggplot2")
data(SrE.IR)
myt <- expression(bolditalic(Serenoa) ~ bolditalic(repens) ~ bold(Extract ~ IR ~ Spectra))
p1 <- surveySpectra(SrE.IR, method = "iqr")
#>
#> Group EPO has 3 or fewer members
#> so your stats are not very useful...
#> This group has been dropped for display purposes!
#>
#> Group OO has 3 or fewer members
#> so your stats are not very useful...
#> This group has been dropped for display purposes!
p1 <- p1 + ggtitle(myt)
p1
p2 <- surveySpectra2(SrE.IR, method = "iqr")
p2 <- p2 + ggtitle(myt)
p2
```