A question regarding the ability to transfer of data between SAS and R set me off on a spot of investigation a while back and I have always planned to share the results of my labours. Once I managed to locate the required documentation, things became clearer with further inspection. Functions from the foreign package seem to offer the most from the data import and export point of view so they’re what I’ll be featuring in this posting.
I’ll start with importing and using the read.ssd function makes life so much easier for getting SAS data into R. I discovered that the foreign package may not be loaded by default but you can determine this easily by issuing the following command:
search()
If "package:foreign" isn’t in the list, then you need to issue the following function call:
library(foreign)
Of course, if the foreign package isn’t installed, none of this will work. It should live in the library sub-folder of the main R installation directory but if it isn’t there, then downloading the relevant binary package from CRAN is in order. Assuming that all is installed, then a command like the following will perform the needful:
read.ssd("c:/data","data1",sascmd="C:/Program Files/SAS Institute/SAS/V8/sas.exe")
This creates a temporary SAS program that converts the SAS data set into a transport file for reading by another R function that is called in the background, read.xport. Form my experience, it all seems to work fairly seamlessly.
To get data out of R and into SAS is a multi-stage process, even with the foreign package. There are other ways but using the write.foreign seems more useful than most and here’s an example function call:
write.foreign(data1,"C:/test.txt","C:/test.sas",package="SAS",dataname="data1",validvarname="V7")
No SAS data sets are created at this stage but a text file is generated along with a SAS program for converting it into a data set. Running the SAS program is a separate step that follows the creation of the two files. Even if it is less streamlined than read.ssd, write.foreign does make easier to transfer data into SAS than having to write a program from scratch to read in write.table output.
In summary, R can neither read or write SAS data sets by itself so you need SAS installed to really make things happen. SAS gets called by read.ssd and I feel that it would be better if was called by write.foreign also rather than a SAS program generated for execution later on. Even so, it is good to see some custom functionality being provided that makes life easier. There’s also the hmisc package but my experiences while working with that on S-Plus have been such that it compares less favourably with foreign on the reliability front. Saying that, things may have changed since I last tried it.
