# [R] for loop query

Gerard M. Keogh GMKeogh at justice.ie
Tue Dec 9 12:43:18 CET 2008

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Hi all,

apologies if this is obvious - but I can't see it and would appreciate some
quick help!

the matrix mhouse is 26x3 and I'm computing odds ratios. The simple code
below "should" compute the odds vector for every pair (325) i.e. 26C2 in
cols 1 and 2.
On the first i=1 outer loop the inner j loop runs from 2 to 26 ok and then
I get the error (Error: subscript out of bounds)

Why isn't my loop incrementing i - the outer loop to 2 and then resetting
j=3?
Am I missing something obvious?

thanks

Gerard

> mhouse
[,1] [,2]  [,3]
[1,]  275  819    49
[2,]  593 1323   192
[3,]  813 1181   292
[4,] 2177 5189  1320
[5,] 1651 2243   270
[6,] 1061 5629 11035
[7,] 1690 2302   589
[8,] 1130 1203   345
[9,]  565 1898   655
[10,]  580  730   234
[11,]  343 1761    73
[12,]  372  536    67
[13,]  666 1713   397
[14,]  382  918   279
[15,]  486  921   247
[16,] 1141  988   313
[17,]  626 1135   666
[18,]  438  436   168
[19,]  425  691   101
[20,]  609  716    99
[21,]  467  661   141
[22,]  879 1373    79
[23,]  444 1101   130
[24,]  459  898   351
[25,]  995 1801   398
[26,]  396 1107   201
> # set up the odds vector by declaring it to be null
> odds=NULL
>
> # compute the odds ratios for Individual House vs Scheme House
> for (i in 1:25)
+ {
+   for (j in i+1:26)
+   {
+     todds = (mhouse[i,1]*mhouse[j,2])/(mhouse[j,1]*mhouse[i,2])
+ #                     compute the todds for row i with row j:
j>i
+     odds = c(odds,todds)
+ #                     append todds to the odds vector
+   }
+ }
Error: subscript out of bounds
> odds
[1] 0.7491244 0.4877622 0.8003391 0.4561745 1.7814132 0.4573697
0.3574670 1.1279674 0.4226138 1.7239078 0.4838053
[12] 0.8636384 0.8069156 0.6363150 0.2907502 0.6087939 0.3342421
0.5459312 0.3947703 0.4752623 0.5244818 0.8326321
[23] 0.6569199 0.6077702 0.9386447
>

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