On Mar 17, 2012, at 2:36 PM, Diann Prosser wrote:
Hi All,
I want to draw samples (n=4) from one of 2 triangular distributions
for
each value in a matrix. I am using an ifelse statement to try to
define
which distribution to draw from.
From the output, I can see that the ifelse statement is choosing
the correct
distribution, however, my n=4 simulations aren't occurring. Is there
a way
to adjust the ifelse statement to fix this, or must I take an entirely
different approach? Many thanks for your help.
matrx <- matrix(c(2, 1, 1, 2, 2,1), nc=nx)
matrx
[,1] [,2] [,3]
[1,] 2 1 2
[2,] 1 2 1
# rtriang from mc2d package: function (n, min = -1, mode = 0, max =
1)
* dmatrx<- ifelse(matrx==1, rtriang(4, min=0.001, mode=matrx,
max=2.001),
rtriang(4, min=2, mode=matrx, max=3))*
Warning message:
In rtriang(4, min = 2, mode = matrx, max = 3) : NaN in rtriang
dmatrx
[,1] [,2] [,3]
[1,] 2.7627761 1.305099 2.7627761
[2,] 0.6158242 2.218274 0.6158242
#(this output should have 4 times as many elements)
If you want four elements then ifelse is the wrong function. It
returns a _vector_, not a matrix. If you want a 2 * 3 * 4 array then
you need to use functions appropriate to the purpose. You didn't
provide 'rtriang', but that's not the issue and this illustrates one
approach.
> sapply(matrx, function(x) if( x==1){rnorm(4)} else {rnorm(4)})
[,1] [,2] [,3] [,4] [,5]
[1,] -0.8829560 -0.1173966 -1.3558024 0.2699102 -0.1267338
[2,] -1.5167439 1.2650024 0.2373172 -1.5316328 -1.8418345
[3,] -0.1196694 0.8097693 -0.4223064 0.1053030 0.9030908
[4,] -1.0486071 -0.2470492 -0.5942510 -0.6877101 0.7017433
[,6]
[1,] -0.5026799
[2,] -4.0098848
[3,] -2.4630189
[4,] -0.6529206
--
David Winsemius, MD
West Hartford, CT
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