Using gnrnd4 on a PC
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This page describes the purpose of and the use of a set of routines encompassed
in the file gnrnd4.R. The purpose and use are strictly related
to the material of this course and in particular, to the coordination of
data values on many of the web pages in this course and
obtaining the same values in an R session.
There are many times when web pages in this course
make reference to a collection of data values.
For example, consider the
Now, although the particular web page may wish to talk about
this data, it would be even better, and in the case of tests on web pages it may be
highly desirable, if you could create a vector of the same values on
your computer, and to do so in R.
If the web page is being displayed on a computer, then one
possible solution would be to highlight the data in the table,
copy it, and paste it to a file.
Were we to do that then the file would have
values in a number of rows and in a number of columns.
R would have a hard time reading that directly, but we could manage it, with
a lot of extra work.
We would have to find some way to read that into R.
Another solution would be to copy the contents of the table
and paste it into some program such as Microsoft Excel,
where we could manipulate the data until we could write it
to a file in a form that R could read.
Of course, neither of those solutions would be of any help
if we were reading Table 1 on paper, as would be the case for a test.
The obvious solution would be to just type the values into R.
We have already seen the command to do this, namely:
But who wants to type that?
In fact, I am sure that I couldn't type that without making at least one error!
One interesting note here is that rather than being presented in table format
if the values were presented as a
comma separated list, such as we just saw in the command above, then we
would have an easier time, using Excel, in converting them to a form
that we could eventually read into R.
But that still does not help in the printed version of the collection of values.
The values given in Table 1 above are generated, each time the page is loaded or refreshed,
by a Javascript program that is part of this web page.
In fact, if you were to use your browser to look at the page source
then you would be able to find and read that Javascript program.
The gnrnd4 solution to our challenge is just a function in R
that performs exactly the same computations as did the Javascript program.
Such a R function is provided in the
file gnrnd4.R. The trick is
- to get that file
- to load it into R
so that you can use it
- to give the R function the starting point
used by the Javascript program to generate the values.
There are a number of ways to achieve points 1 and 2.
On my web page there is a listing that gives all of the
routines that I have written for this course.
It is on the page
Table of Links to various R scripts.
Part of that table provides a link to eaach of the routines.
You could use that link to download the file to your computer
and then
copy it into any R session that you are using.
A second approach would be to configure a R
command that would directly read the file from my web site.
The R command to do that is
source("http://courses.wccnet.edu/~palay/math160r/gnrnd4.R")
The third approach, and the one I want us to use,
takes into account the fact that the USB drive given out in
class actually has the desired file on it.
You can have R load the file from that drive.
The steps that follow walk you through doing this.
Our goal will be to generate the values in the following table:
The eventual command that we will use to generate these same values
in our R session is
gnrnd4(key1=364527804,key2=1600123). However, we
want to do a number of steps to set up all of this.
The work here was done on a PC running Windows 10.
We start by inserting the USB drive. Windows opens
File Explorer to give us a view of the contents of the drive.
The top of that view is shown in Figure 0.
Figure 0
If the expanded menu shown in Figure 1 is not visible, just click on the
Home menu item, circled in green in Figure 1, to display that
expaned menu.
Within that menu we want to click on the
Few Folder icon as shown in Figure 1.
Figure 1
This creates a new filder with the default name New folder,
a name we would like to change now.
Figure 2
Because the name New folder is highlighted in Figure 2
we can just enter our new name; in this eample we will
call it project02, as shown in Figure 3.
Figure 3
Our next step is to get a copy of the file
model.R from the top directory (folder) of our USB drive.
Figure 3 is still displaying that top directory.
Therefore, we point to the file name, model.R,
and "right-click" on that file name. This opens an
action pane shown in Figure 4.
Figure 4
Of all the actions shown, the one we want is Copy.
To do this we just click on that action.
At this point the computer has a copy of the file.
We want to put that copy into our new directory, project02.
To do this we need to navigate to that new directory.
We do this by doublie clicking on the
directory name, as shown in Figure 5.
Figure 5
This causes File Explorer to display the contents
if the project02 foldere, shown in Figure 6.
Figure 6
As expected, since we just created the folder, it is empty.
But not for long.
We just right-click in th files area of Figure 6 and this opens a new
actions pane, shown in Figure 7.
Figure 7
There we click on the Paste option. The result, shown in Figure 8,
is that we now have a copy of model.R in our new
sub-directory, project02.
Figure 8
Now we want to change the name of the file to
something more appropriate. We point to the name in Figure 8 and then
right click on it to open the action window shown in Figure 9.
Figure 9
Click on the Rename option. This will highlight the file
name, as shown in Figure 9a.
Figure 9a
Then type in the new name,
we will use the name demo_gnrnd4.R
and we get Figure 10.
Figure 10
Then we double click on that file name, shown in Figure 10a,
in order to open our RStudio session.
Figure 10a
Figure 11 shows the entire RStudio window.
Figure 11
If we look, in Figure 12, at the upper left pane, the editor pane,
we see that RStudio has opened our new file, demo_gnrnd4.R.
Figure 12
Note, in Figure 12, that there is another file,
in this instance base.R, that is in this editor.
This is left over from an
earlier run of RStudio. We do not want this file in this session.
Therefore we click on the little "x" after that file
name in order to close it. That leaves us with just the
demo_gnrnd4.R file in the editor, as shown in Figure 13.
Figure 13
If we turn our attention to the
lower left pane of Figure 11, we seeFigure 14.
IF you are following alon g on your own computer you
may not see any of the red warning message.
That red warning message is in Figure 14 because I had no internet connection
while I was doing this session. Since we have no need for an internet connection
in this eample, the warning can be ignored.
Figure 14
The environment pane, shown in Figure 15, is empty.
That is a result of our having started in a new folder, project02,
without any previous run of R in this folder.
We are starting with a clean slate.
Figure 15
Returning to the editor pane, we want to type some new comment lines
and then type the one command source("../gnrnd4.R") as shown in
Figure 16. To make life a bit easier for you, the lines are
#This is an example of using gnrnd4.
# I have a web page that tells me that I can generate
# specific data values in a given table by using
# the gnrnd4 routine with given arguments.
# I will try it here.
# First we need to get the gnrnd4 routine into our
# current environment. the routine is on this USB
# drive, in the directry (folder) directly above
# this one. So we use the command
source("../gnrnd4.R")
If you are following allon on your own computer you can copy
the lines from this web page and just paste them into your
RStudio session.
Figure 16
Figure 17 shows just lines 11 and 12 of Figure 16.
Notice that the cursor is on line 12,
the line containing the command that we want to run.
To run that command click on the
at the top of the
editor pane, circled back in Figure 16.
Figure 17
The result, shown in the console pane in Figure 17a,
is that the command is run in R. It produces no output.
Figure 17a
However, if we return to the environment pane,
Figure 18, we see that two new values and two new functions
have been defined.
Figure 18
Now that the function has been loaded into our environment we can
actually use it. Figure 19 shows the new lines that we have
added in the editor pane. They are reproduced here so that you can copy them if so desired into your
RStudio session.
# once it is loaded we can use it. The two
# arguments that we were given were
# key1=364527804 and key2=1600123. We use those
# to make the command
gnrnd4(key1=364527804,key2=1600123)
Figure 19
In Figure 19 we have hghlighted the command that we actually want to execute.
We click on the 
to actually run that hghlighted command.
The result is seen, in the console pane, in Figure 20.
Figure 20
This time there was actually some output, but its meaning is not
completely clear. On the other hand, if we look back at the
environment pane, shown in Figure 21, we see that we now have two new
variables, one of which, L1, seems to hold the
numbers from Table 2 that we were trying to
create in our RStudio session.
Figure 21
If we want to see all of the contents of L1 we can just use
that variable name. As has been our practice we will first add it to the editor
pane. That is done in Figure 22.
Figure 22
Then, using the ![]()
we have
RStudio perform that command in the console
pane shown in Figure 23.
Figure 23
At this point we are essentially done. We can give the command
q() directly in the console
pane as shown in Figure 24.
Figure 24
When we try to quit the session RStudio recognizes that we have been adding things to
the file in the editor, namely, to the file demo_gnrnd4.RRStudio does not want us to accidently lose our work so it gives
us the opetion, shown in Figure 25, to save that file.
Figure 25
Once we click on the Save button in Figure 25 RStudio returns us to the
console pane where R asks if we want to save the workspace. We
respond in Figure 26 wth a y.
Figure 26
Pressing e Enter key concules our RStudio session.
this also returns us to the File explorer
screen which now shows the current
contents of our directory project02.
Figure 27
The conents of Figure 27 seem a little strange. First of all there are now three
files in the directory. The file demo_gnrnd4.R is expected. you might note that it has now
grown to be 1KB long. The other two files remain a bit of a mystery
with the last one showing up as and icon but without even a name.
This last issue is caused, in this case, because the computer on which this was
run did not have the File name extensions switch turned on.
We can fix that problem by first clicking on the
View menu option. That will display the action
menu shown in Figure 28.
Figure 28
Click on the box before File name extensions and the display changes
to that of Figure 29.
Figure 29
Now we see that the two new files are .Rhstory and .RData.
OF those two, .RData holds the variables and functions that we had in the
environment back in Figure 26 when we closed our session.
If we now double click on the demo_gnrnd4.R file,
we will start a new RStudio session, but this time it will start with the environment
the way we left it back in Figure 26. You can see this in Figure 30.
Figure 30
We close our RStudio session with the q() command.
Here is the list of commands used on this page:
#This is an example of using gnrnd4.
# I have a web page that tells me that I can generate
# specific data values in a given table by using
# the gnrnd4 routine with given arguments.
# I will try it here.
# First we need to get the gnrnd4 routine into our
# current environment. the routine is on this USB
# drive, in the directry (folder) directly above
# this one. So we use the command
source("../gnrnd4.R")
# once it is loaded we can use it. The two
# arguments that we were given were
# key1=364527804 and key2=1600123. We use those
# to make the command
gnrnd4(key1=364527804,key2=1600123)
# The routine createdd the values in the variabe L1
# We will look at that variable
L1
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©Roger M. Palay
Saline, MI 48176 September, 2017