Import Data into a Spectra2D Object

This function imports data into a Spectra2D object. It primarily uses read.table to read files so it is very flexible in regard to file formatting. Be sure to see the ... argument below for important details you need to provide.

files2Spectra2DObject(
  gr.crit = NULL,
  gr.cols = "auto",
  fmt = NULL,
  nF2 = NULL,
  x.unit = "no frequency unit provided",
  y.unit = "no frequency unit provided",
  z.unit = "no intensity unit provided",
  descrip = "no description provided",
  fileExt = "\\.(csv|CSV)$",
  out.file = "mydata",
  debug = 0,
  chk = TRUE,
  allowSloppy = FALSE,
  ...
)

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.crit or there are entries in gr.crit that don't match any file names.
gr.cols	Group Colors. See colorSymbol for some options. One of the following: Legacy behavior and the default: The word "auto", in which case up to 8 colors will be automatically assigned from package RColorBrewer Set1. "Col7". A unique set of up to 7 colorblind-friendly colors is used. "Col8". A unique set of up to 8 colors is used. "Col12". A mostly paired set of up to 12 colors is used. A vector of acceptable color designations with the same length as gr.crit. Colors will be assigned one for one, so the first element of gr.crit is assigned the first element of gr.col and so forth. For Col12 you should pay careful attention to the order of gr.crit in order to match up colors. See colorSymbol for further details.
fmt	A character string giving the format of the data. Consult import2Dspectra for options. If fileExt is one of dx, DX, jdx or JDX, fmt will automatically be set to "dx" and package readJDX will be used for the import. In this case check the values of F2 and F1 carefully. The values are taken from the file, for some files/vendors the values might be in Hz rather than ppm.
nF2	Integer giving the number of data points in the F2 (x) dimension. Note: If any dimension is zero-filled you may need to study the acquistion details to get the correct value for this argument. This may be vendor-dependent.
x.unit	A character string giving the units for the F2 dimension (frequency or wavelength corresponding to the x dimension).
y.unit	A character string giving the units for the F1 dimension (frequency or wavelength corresponding to the y dimension).
z.unit	A character string giving the units of the z-axis (some sort of intensity).
descrip	A character string describing the data set.
fileExt	A character string giving the extension of the files to be processed. regex strings can be used. For instance, the default finds files with either ".csv" or ".CSV" as the extension. Matching is done via a grep process, which is greedy. If fileExt is one of dx, DX, jdx or JDX, fmt will automatically be set to "dx" and package readJDX will be used for the import.
out.file	A file name. The completed object of S3 class Spectra2D will be written to this file.
debug	Integer. Set to 1 or TRUE for basic reporting when there are problems. If importing JCAMP-DX files, values greater than 1 give additional and potentially huge output. Once you know which file is the problem, you may wish to troubleshoot directly using package readJDX.
chk	Logical. Should the Spectra object be checked for integrity? If you are having trouble importing your data, set this to FALSE and do str(your object) to investigate.
allowSloppy	Logical. Experimental Feature If TRUE, disable checking of the data set, and return all pieces of the raw import from import2Dspectra in the spectra$data object. The resulting object currently cannot be used by any other functions in this package! The intent is allow importing of spectra that differ slightly in the number of points in each dimension. With this option one can use str on the resulting object to inspect the differences. Future functions will allow one to clean up the data.
...	Arguments to be passed to read.table, list.files or readJDX; see the "Advanced Tricks" section. For read.table, You MUST supply values for sep, dec and header consistent with your file structure, unless they are the same as the defaults for read.table.

Value

One of these objects:

• If allowSloppy = FALSE, the default, an object of class Spectra2D.

• If allowSloppy = TRUE, an object of undocumented class SloppySpectra2D. These objects are experimental and are not checked by chkSpectra. For these objects spectra$F1 and spectra$F2 are NA, and each spectra$data entry is a list with elements F1, F2 and M, which is the matrix of imported data (basically, the object returned by import2Dspectra).

• In each case, an unnamed object of S3 class Spectra2D or SloppySpectra2D is also written to out.file. To read it back into the workspace, use new.name <- loadObject(out.file) (loadObject is package R.utils).

Details

files2Spectra2DObject acts on all files in the current working directory with the specified fileExt so there should be no extraneous files with that extension in the directory.

gr.crit and Sample Name Gotchas

The matching of gr.crit against the sample file names 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 Spectra2D object, but they are not assigned a group. 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

Bryan A. Hanson, DePauw University.