[R] Urgent Help needed

[AbouEl-Makarim Aboueissa]

Dear All:

Urgent help is needed.


I have a data set in matrix format  of three columns: X, Y and index of four groups (1,2,3,4). What I need to do is the following;

1- How I can subtract the sample mean of each group indexed 1,2,3,4 from the 
     corresponding data values of this group and create new columns say X-sample mean 
      and Y-sample mean? I tried to use the "tapply" but I have some difficulties to restore the new data


2- How I can use the “tapply” if possible or any other R-function to find the correlation 
     coefficient between the X and Y columns for each group indexed 1,2,3,4.? Could not use the "tapply".


I attached part of the data as txt file.


Thank you so much for your attention to this matter, and I look forward to hear from you soon.

Regards,

Abou


Data:
====
x	y	index
15807.24 	12.5 	4
15752.51 	33.5 	4
12893.76 	01.5 	3
8426.88 	22.2 	3
5706.24 	333 	3
3982.08 	560 	2
3642.62 	670 	2
295.68 		124 	1
215.40 		104 	1
195.40 		204 	1
4240.21 	22.4 	2
1222.72 	45.9 	2
1142.26 	23.6 	2
63.00 		90.1 	1
1216.00 	82.4 	2
2769.60 	111 	2
1790.46 	34.7 	2
26.10 		26.10 	1
19676.83 	0.99 	4
10920.60 	203 	3
6144.00 	46 	3
4534.48 	4534.48 3
40000.00 	65 	4
29500.00 	56 	4
17100.00 	77 	4
9000.00 	435 	3
6300.00 	84 	3
3962.88 	334 	2
5690.00 	653 	3
3736.00 	233 	2
2750.00 	22 	2
1316.00 	345 	2
4595.00 	4595.00 3
5928.00 	45 	3
2645.70 	0.00 	2
2580.24 	454 	2
6547.34 	6547.34 3
1615.68 	5 	2
194.06 		55 	1
184.80 		6 	1
82.94 		44 	1
16649.00 	56 	4
4500.00 	74 	3
1600.00 	744 	2

=================



==========================
AbouEl-Makarim Aboueissa, Ph.D.
Assistant Professor of Statistics
Department of Mathematics & Statistics
University of Southern Maine
96 Falmouth Street
P.O. Box 9300
Portland, ME 04104-9300

Tel: (207) 228-8389
Email: aaboueissa at usm.maine.edu
          aboueiss at yahoo.com
Office: 301C Payson Smith

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