(According section in the tutorial: 3.2. Data import)
How does R work? By executing code, i.e. by calling functions, mostly with
some arguments. Code can be commented; everything after # is a comment and
will not be executed. You can use this to activate or deactivate code, too:
This will be printed:
message("I like R and opm!")
## I like R and opm!
This would not be printed:
# message("I don't like R and opm!")
5 + 19 # result will be printed to the screen
## [1] 24
result <- 5 + 19 # will not print
result # will print: object `result` now contains 24, assigned to it using `<-`
## [1] 24
5 + 15:20 # what does this do?
## [1] 20 21 22 23 24 25
Note that in R you can pass vectors of length > 1 to most functions, and
they will return a vector of the same length.
result # still there
## [1] 24
rm(result) # deleting it
Entering result would now yield Error: object 'result' not found.
"I am a character string and will be printed to the screen"
## [1] "I am a character string and will be printed to the screen"
TRUE # this means, well, true
## [1] TRUE
FALSE # guess what
## [1] FALSE
NA # this means 'NOT AVAILABLE' (missing data)
## [1] NA
With left-hand side:
x ~ a * y1 + b * y2 - c * y3 ^ 2
## x ~ a * y1 + b * y2 - c * y3^2
## <environment: 0x3a572e8>
Without left-hand side:
~ a * y1 + b * y2 - c * y3 ^ 2
## ~a * y1 + b * y2 - c * y3^2
## <environment: 0x3a572e8>
Formulas are a special kind of code that is not evaluated but stores symbolic representations to be interpreted later on in a specific way.
If anything fails, read the error message!
Now we load and attach the opm functions. Note that if a package such as
opm has already been loaded, the library command does nothing. It thus
can be called at any time.
library(pkgutils)
library(opm)
message("Welcome to R and opm!")
## Welcome to R and opm!
Note that you can call
# ?ITEM
at any time to get the documentation for the topic ITEM (replace ITEM by
what you are interested in). The following command would list the content of
the entire opm documentation:
help(package = "opm")
Now please make sure you are in the right directory! You can call the getwd
command to check that. To change the working directory in RStudio use:
Session > Set Working Directory > To Source File Location.
Because it is important, let us issue a warning about the working directory:
warning("the working directory is ", getwd(), " -- correct?")
## Warning: the working directory is
## /home/goeker/Documents/SVN_opm/trunk/opm_doc/demo -- correct?
A warning is not an error; it does not stop the execution of code.
We assume that only the CSV files within the working directory should be
input and that the data read should be grouped by plate type (see below or
consult the opm manual or tutorial for what that means). The following code
fails if unreadable CSV files are there and not deselected (the include
and/or exclude argument would need to be adapted).
x <- read_opm(
names = getwd(), # search in the working directory for files of interest
convert = "grp", # group the plates according to the plate type
include = list("csv"), # search only for CSV files
exclude = "*template*", # but exclude CSV files that match this pattern
# (we later on generate metadata template CSV files)
demo = FALSE # read the files, do not just show the file names
)
If this fails, read the error message! The most usual error we know about is
to try to input CSV files with several plates per file, but these would
need to be split beforehand, which you can do with opm itself. This works
as follows:
split_files(filename, '^("Data File",|Data File)', getwd())
where filename is the name of the file to be split, provided as character
string. The newly generated files are numbered accordingly. (They are not
named after any metainformation entry because there is no guarantee that it
is present.)
It is of course easier to use single-plate instead of multiple-plate files in
the first place. How to do this is described in the opm tutorial.
The second frequent kind of error is that you attempt to read files that are CSV but do not contain PM data. This can be fixed as follows:
demo = TRUE to first show the files you would read, and if this list
contains names of files that apparently cannot be read by opm, modify the
inclusion or exclusion settings.names argument. This gives you most control
about the files read.The opm package understands several styles of CSV and the new LIMS format.
We now have a look at the resulting object. You do not routinely need all of the following commands; some calls are just for beginners who are curious. Others tell you important features of the generated data object, however.
That command yields MOPMX; if you are curious what that means, consult
figure 4 in the tutorial.
class(x)
## [1] "MOPMX"
## attr(,"package")
## [1] "opm"
As often in R, summary is a quite useful function …
summary(x)
## [1] Length Plate.type Aggregated Discretized
## <0 rows> (or 0-length row.names)
##
## => MOPMX object with 0 element(s), details are shown above.
## Access the elements with [[ or $ to apply specific methods.
… but in opm you can just enter the name of the object, which also shows
the summary:
x
## [1] Length Plate.type Aggregated Discretized
## <0 rows> (or 0-length row.names)
##
## => MOPMX object with 0 element(s), details are shown above.
## Access the elements with [[ or $ to apply specific methods.
Show the distinct input plate types:
names(x)
## character(0)
Names could theoretically be missing in such objects, however, but the next function always works to get the plate type:
plate_type(x)
## character(0)
This command checks for aggregated data (a.k.a. curve parameters); must all
be FALSE:
has_aggr(x)
## NULL
This command shows the metainformation that was directly found in the CSV files:
csv_data(x)
## NULL
The next R instruction shows the proper metadata (none there yet!):
metadata(x)
## NULL
It makes no sense to proceed if we have not input any data. This happens if no suitable files are found.
length(x) > 0
## [1] FALSE
If you have only one plate type, you could simplify the object:
# x <- x[[1]] # fetches the 1st element, which belongs to the sole plate type
# class(x) # yielded `OPMS` or `OPM`; if you are curious, consult figure 4 in
# # the tutorial
But this is not normally necessary.
Now proceed with part 2.