Hi,
The great thing about the S language is that it is 'vectorized',
so you can do a lot of matrix manipulations without loops.
Here's a smaller example of what you describe.
matrix A with 3 columns and 10 rows (instead of 100)
matrix B with 3 columns and 15 rows (instead of 1500)
> set.seed(123)
> mA <- matrix(runif(30), ncol = 3)
> mA
[,1] [,2] [,3]
[1,] 0.2875775 0.95683335 0.8895393
[2,] 0.7883051 0.45333416 0.6928034
[3,] 0.4089769 0.67757064 0.6405068
[4,] 0.8830174 0.57263340 0.9942698
[5,] 0.9404673 0.10292468 0.6557058
[6,] 0.0455565 0.89982497 0.7085305
[7,] 0.5281055 0.24608773 0.5440660
[8,] 0.8924190 0.04205953 0.5941420
[9,] 0.5514350 0.32792072 0.2891597
[10,] 0.4566147 0.95450365 0.1471136
> x <- seq(15)
> mB <- cbind(1, x, x^2)
> mB
x
[1,] 1 1 1
[2,] 1 2 4
[3,] 1 3 9
[4,] 1 4 16
[5,] 1 5 25
[6,] 1 6 36
[7,] 1 7 49
[8,] 1 8 64
[9,] 1 9 81
[10,] 1 10 100
[11,] 1 11 121
[12,] 1 12 144
[13,] 1 13 169
[14,] 1 14 196
[15,] 1 15 225
> mR <- apply(mB, 1, function(x){mA %*% x})
> mR
[,1] [,2] [,3] [,4] [,5] [,6] [,7]
[1,] 2.133950 5.759401 11.163931 18.347540 27.310227 38.05199 50.57284
[2,] 1.934443 4.466187 8.383538 13.686496 20.375061 28.44923 37.90901
[3,] 1.727054 4.326145 8.206250 13.367368 19.809500 27.53265 36.53681
[4,] 2.449921 6.005363 11.549346 19.081867 28.602929 40.11253 53.61067
[5,] 1.699098 3.769140 7.150594 11.843459 17.847736 25.16342 33.79052
[6,] 1.653912 4.679328 9.121806 14.981344 22.257943 30.95160 41.06232
[7,] 1.318259 3.196545 6.162963 10.217513 15.360195 21.59101 28.90995
[8,] 1.528621 3.353106 6.365876 10.566930 15.956267 22.53389 30.29979
[9,] 1.168515 2.363915 4.137635 6.489674 9.420032 12.92871 17.01571
[10,] 1.558232 2.954077 4.644149 6.628448 8.906974 11.47973 14.34671
[,8] [,9] [,10] [,11] [,12] [,13] [,14]
[1,] 64.87276 80.95176 98.80984 118.44700 139.86324 163.05856 188.03295
[2,] 48.75440 60.98539 74.60199 89.60419 105.99201 123.76542 142.92445
[3,] 46.82198 58.38816 71.23536 85.36358 100.77281 117.46305 135.43430
[4,] 69.09735 86.57257 106.03633 127.48863 150.92947 176.35884 203.77676
[5,] 43.72904 54.97896 67.54029 81.41304 96.59720 113.09277 130.89975
[6,] 52.59011 65.53495 79.89685 95.67582 112.87184 131.48493 151.51508
[7,] 37.31703 46.81224 57.39559 69.06706 81.82667 95.67440 110.61027
[8,] 39.25398 49.39646 60.72722 73.24626 86.95358 101.84919 117.93309
[9,] 21.68102 26.92466 32.74662 39.14689 46.12549 53.68240 61.81763
[10,] 17.50792 20.96335 24.71302 28.75691 33.09502 37.72737 42.65394
[,15]
[1,] 214.78642
[2,] 163.46908
[3,] 154.68657
[4,] 233.18322
[5,] 150.01814
[6,] 172.96229
[7,] 126.63428
[8,] 135.20527
[9,] 70.53119
[10,] 47.87474
>
so the results matrix mR has one column for each element of x,
and the i-th row element is the solution for
y = a + bx + cx^2
for the i-th row of coefficients in the parameter estimates matrix mA
You can spot check with e.g.
> mA[1,] %*% mB[15,]
[,1]
[1,] 214.7864
> mA[1,] %*% mB[5,]
[,1]
[1,] 27.31023
> mA[1,]
[1] 0.2875775 0.9568333 0.8895393
> mB[5,]
x
1 5 25
>
HTH
Steven McKinney, Ph.D.
Statistician
Molecular Oncology and Breast Cancer Program
British Columbia Cancer Research Centre
email: smckinney +at+ bccrc +dot+ ca
tel: 604-675-8000 x7561
BCCRC
Molecular Oncology
675 West 10th Ave, Floor 4
Vancouver B.C.
V5Z 1L3
Canada
________________________________________
From: r-help-boun...@r-project.org [r-help-boun...@r-project.org] On Behalf Of
Jessica Schedlbauer [jsche...@fiu.edu]
Sent: November 25, 2009 10:43 AM
To: r-help@r-project.org
Subject: [R] help writing for loop
Hi,
I’d like to ask for some help in writing a loop. My situation is the following:
I have a matrix (matrix.A) containing 3 columns and 100 rows. The columns
represent parameter estimates a, b, and c. The rows contain different values
for these parameter estimates. Each row is unique.
I want to insert these parameter estimates into a model (say, y = a + bx +
cx^2) and solve for y given a separate matrix (matrix.B) of x values (where x
has a length of 1500).
I want to solve for y 100 times using each set of the parameter estimates in
matrix.A once.
At present my code looks like this and it only performs the first iteration.
For (i in 1:length(matrix.A)) { y <- matrix.A$a[[i]] + matrixA$b[[i]] *
matrix.B$x + matrixA$c[[i]] * matrix.B$x^2)
I have not been able to figure out how to loop through the rows of parameter
estimates in matrix.A. I am new to writing loops, so any assistance would be
much appreciated.
Regards,
Jessica Schedlbauer
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______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
