| files2SpectraObject {ChemoSpec} | R Documentation |
Import Data into a Spectra Object
Description
These functions import data into a Spectra object. For "csv-like" files they use
read.table, so they are very flexible in regard to file formatting.
Be sure to see the ... argument below for important details you need to provide.
files2SpectraObject can also read JCAMP-DX files and will do so if fileExt is
any of "dx", "DX", "jdx" or "JDX".
Usage
files2SpectraObject(
gr.crit = NULL,
gr.cols = "auto",
freq.unit = "no frequency unit provided",
int.unit = "no intensity unit provided",
descrip = "no description provided",
fileExt = "\\.(csv|CSV)$",
out.file = "mydata",
debug = FALSE,
...
)
matrix2SpectraObject(
gr.crit = NULL,
gr.cols = c("auto"),
freq.unit = "no frequency unit provided",
int.unit = "no intensity unit provided",
descrip = "no description provided",
in.file = NULL,
out.file = "mydata",
chk = TRUE,
...
)
Arguments
gr.crit |
Group Criteria. A vector of character strings which will be
searched for among the file/sample names in order to assign an individual
spectrum to group membership. This is done using grep, so characters
like "." (period/dot) do not have their literal meaning (see below).
Warnings are issued if there are file/sample names that don't match entries in
|
gr.cols |
Group Colors. See
Colors will be assigned one for one, so the first element of
|
freq.unit |
A character string giving the units of the x-axis (frequency or wavelength). |
int.unit |
A character string giving the units of the y-axis (some sort of intensity). |
descrip |
A character string describing the data set that will be stored. This string is used in some plots so it is recommended that its length be less than about 40 characters. |
fileExt |
A character string giving the extension of the files to be
processed. |
out.file |
A file name. The completed object of S3 class |
debug |
Logical. Applies to |
... |
Arguments to be passed to |
in.file |
Character. Applies to |
chk |
Logical. Applies to |
Value
A object of class Spectra. An unnamed object
of S3 class Spectra is also written to out.file. To
read it back into the workspace, use new.name <- loadObject(out.file)
(loadObject is package R.utils).
Functions
-
files2SpectraObject(): Import data from separate csv files -
matrix2SpectraObject(): Import a matrix of data
files2SpectraObject
files2SpectraObject acts on all files in the current working
directory with the specified fileExt so there should be no
extra files of that type hanging around (except see next paragraph).
The first column should contain the frequency values and the second column the intensity values. The
files may have a header or not (supply header = TRUE/FALSE as
necessary). The frequency column is assumed to be the same in all files.
If fileExt contains any of "dx", "DX", "jdx" or
"JDX", then the files will be processed by readJDX.
Consider setting debug = TRUE, or debug = 1 etc for this format, as there are many
options for JCAMP, and many are untested. See readJDX for options and
known limitations.
matrix2SpectraObject
This function takes one or more csv-like files, containing frequencies in the first
column, and samples in additional columns, and processes it into a
Spectra object. The file MUST have a header row which includes
the sample names. There need not be a header for the first (frequency)
column. If more than one file given, they must all have the same frequency entries.
gr.crit and Sample Name Gotchas
The matching of gr.crit against the sample file names
(in files2SpectraObject) or column headers/sample names
(in matrix2SpectraObject) is done one at
a time, in order, using grep. While powerful, this has the potential to lead
to some "gotchas" in certain cases, noted below.
Your file system may allow file/sample names which R will not like, and will
cause confusing behavior. File/sample names become variables in ChemoSpec, and R
does not like things like "-" (minus sign or hyphen) in file/sample names. A hyphen
is converted to a period (".") if found, which is fine for a variable name.
However, a period in gr.crit is interpreted from the grep point of view,
namely a period matches any single character. At this point, things may behave
very differently than one might hope. See make.names for allowed
characters in R variables and make sure your file/sample names comply.
The entries in gr.crit must be
mutually exclusive. For example, if you have files with names like
"Control_1" and "Sample_1" and use gr.crit = c("Control", "Sample")
groups will be assigned as you would expect. But, if you have file names
like "Control_1_Shade" and "Sample_1_Sun" you can't use gr.crit =
c("Control", "Sample", "Sun", "Shade") because each criteria is grepped in
order, and the "Sun/Shade" phrases, being last, will form the basis for your
groups. Because this is a grep process, you can get around this by using
regular expressions in your gr.crit argument to specify the desired
groups in a mutually exclusive manner. In this second example, you could
use gr.crit = c("Control(.*)Sun", "Control(.*)Shade", "Sample(.*)Sun",
"Sample(.*)Shade") to have your groups assigned based upon both phrases in
the file names.
To summarize, gr.crit is used as a grep pattern, and the file/sample names
are the target. Make sure your file/sample names comply with make.names.
Finally, samples whose names are not matched using gr.crit are still
incorporated into the Spectra object, but they are not
assigned a group or color. Therefore they don't plot, but they do take up space in a
plot! A warning is issued in these cases, since one wouldn't normally want
a spectrum to be orphaned this way.
All these problems can generally be identified by running sumSpectra
once the data is imported.
Advanced Tricks
The ... argument can be used to pass any argument to read.table or list.files.
This includes the possibility of passing arguments that will cause trouble later, for instance
na.strings in read.table. While one might successfully read in data with NA,
it will eventually cause problems. The intent of this feature is to allow one to recurse
a directory tree containing the data, and/or to specify a starting point other than the current
working directory. So for instance if the current working directory is not the directory containing
the data files, you can use path = "my_path" to point to the desired top-level
directory, and recursive = TRUE to work your way through a set of subdirectories. In addition,
if you are reading in JCAMP-DX files, you can pass arguments to readJDX via ..., e.g. SOFC = FALSE.
Finally, while argument fileExt appears to be a file extension (from its
name and the description elsewhere), it's actually just a grep pattern that you can apply
to any part of the file name if you know how to construct the proper pattern.
Author(s)
Bryan A. Hanson (DePauw University).
See Also
Additional documentation at https://bryanhanson.github.io/ChemoSpec/,
as well as updateGroups.
Examples
## Not run:
# This example assumes the graphics output is set to ggplot2 (see ?GraphicsOptions).
library("ggplot2")
wd <- getwd() # save current location
setwd(tempdir())
# Grab an included file & move to a temporary directory
tf <- system.file("extdata/PCRF.jdx", package = "ChemoSpec")
chk <- file.copy(from = tf, to = basename(tf))
# Now read in the file, summarize and plot
spec <- files2SpectraObject(
gr.crit = "PCRF", freq.unit = "ppm", int.unit = "intensity",
descrip = "test import", fileExt = "\\.jdx")
sumSpectra(spec)
p <- plotSpectra(spec, lab.pos = 3.5, main = "Reduced Fat Potato Chip")
p <- p + ggtitle("Reduced Fat Potato Chip")
p
setwd(wd) # restore working directory
## End(Not run)