(1) Loading a library is necessary to use the downloaded and installed package. Remember, the terms package and library are used synonymously throughout R literature; however, one could say a package becomes a library when it is loaded. In the previous set of notes, we downloaded and installed the Hmisc package (hopefully you have all packages by now). To use a package, we must now load it. This is a very simple procedure; in the console, simply type the following and hit enter.

library(Hmisc)

Any downloaded and installed package can be loaded by typing: library(name) where ‘name’ refers to the package name. Occasionally, when a package loads, it will ‘mask’ objects in other packages and the R console will return a message for each library loaded. As an example, consider the following; package Hmisc will mask the object ‘recode’ in package car if car is already loaded. This bears watching because; it can be extremely frustrating when attempting to use a familiar function which will no longer work because a newly loaded package is masking it. The good news is that this does not occur frequently even when using many libraries (e.g. multiple libraries can be loaded and used simultaneously). For this reason, it can be important and preferable to clean up after one’s self by using the ‘detach’ library command for libraries which are not being used.

(2) Detach a library. Again, it is extremely easy to detach a library which is no longer needed. Simply type the following and hit enter:

detach(“package:Hmisc”)

Common errors result from forgetting the parentheses and/or quotations, as well as forgetting the colon between package and the library name. As an exercise in ensuring we are doing what we think we are doing, type the following and hit enter:

search()

The search function shows all the loaded libraries. Notice, Hmisc is not listed. Now hit your up arrow 3 times and then hit the enter key. Notice, the up arrow scrolls through your previous commands and the third command up should have been ‘library(Hmisc)’. When you hit the enter key, you should have loaded that library again. So, if we hit the up arrow twice, we should see the ‘search()’ command and if we hit enter again, we should see that Hmisc is listed as a loaded package. Also notice that the ‘base’ package is loaded; which as the name implies is part of the base install of R and is loaded when the program R is opened/started.

(3) Preloading libraries. It can be very convenient to have one or a few libraries load when you start R if you tend to use these libraries during every session. This is the same rationale behind the base library being loaded each time R starts; everyone uses it every time they use R. You can customize R to load certain libraries upon start up by locating a file called “Rprofile.site” which by default is located in:

C:\Program Files\R\R-x.xx.x\etc

where x.xx.x refers to the version number of the R installation you are using (e.g. R-2.14.0) and yes, there is an ‘etc’ folder. Once you locate the Rprofile.site file, you can open it in Notepad which by default is available with each installation of Windows. Here is where you can tell R to load certain libraries upon start up. As an example, you can see my current Rprofile.site file here. One thing to notice in my Rprofile is the line:

setwd("c:\\Documents and Settings\\jons\\Desktop\\Work_Stuff\\Jon_R")

which sets the working directory for R. This tells R where to start looking when ever you go to File and open or save in R. In other words, if you wanted to open or save something from the R console, it will start with the specified working directory. You can set your working directory to be any folder on your computer.

*Important Note: If you change your Rprofile to preload libraries at start up, it will be necessary to cut and paste the Rprofile file from the ‘etc’ folder to some other location prior to starting R when you want to update packages. For instance, after having R and all packages downloaded and installed for a week, you will likely want to check for updates. Then, go to the ‘etc’ folder and cut the Rprofile file out and paste it to your desktop. Then, start R and update packages/libraries as mentioned previously. Yes, the program will function without that file. After updating all packages, then close R. Then, cut the Rprofile file off your desktop and paste it back into the ‘etc’ folder…then restart R. The reason you would need to do this is because, R will not update packages/libraries that are in use (i.e. loaded). So, if you have your Rprofile set to load some libraries at start up, you would never be able to update those libraries.

So, you’re probably wondering what’s in a library? We’ll answer that in the next set of notes.