[R] grouping data by a portion of the row name

[Bricklemyer, Ross S]

I am attempting to write a routine where I can run PAM (partition around mediods) on a dataset containing multiple soil cores and PCA spectral data from several depths per core.  I want to run PAM on each individual core, so I need to group the data by core to run the analysis.  Below is an example of my data structure:

Lab.id	PC1	PC2	PC3
MAT057.2.5	2.438454966	-1.011182986	-3.040881377
MAT057.7.5	10.69120648	4.767694892		-1.719466898
MAT057.12.5	8.215852171	4.645793327		0.974020242
MAT057.17.5	10.00422215	3.516213164		2.586742695
MAT057.22.5	18.49165113	5.143031557		0.472636009
MAT057.27.5	18.31255522	4.255319595		0.802902692
MAT057.35	11.75818601	-0.325388031	3.445673092
MAT057.45	6.043984786	-3.297325975	3.075221644

The MAT057 is the core code and the values following the period refer to the sampling depths.  There are many cores in the dataset and I want to automate the analysis so that it will grab data with the same core code and run PAM.  Any ideas on what the R code would look like for that?

Ross

*******************************************************************
Ross Bricklemyer
Dept. of Crop and Soil Sciences
Washington State University
291D Johnson Hall
PO Box 646420
Pullman, WA 99164-6420
Work: 509.335.3661
Cell/Home: 406.570.8576
Fax: 509.335.8674
Email: rsb at wsu.edu