Hi
start simple!
Work out *each* row combined with *each* row,
to give (in your case) a 26-by-26 matrix.
Only after you have got this working, start thinking about
making it run faster [eg by
only evaluating the upper triangular entries]
To do a nested loop, do
M <- matrix(0,n,n)
for(i in seq_len(n)){
for(j in seq_len(n)){
M[i,j] <- f(i,j)
}
}
which will fill in matrix M for you.
HTH
rksh
Gerard M. Keogh wrote:
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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