Problem with pmax and matrix to calculate row maxima
Hi Wolfgang,
how about a loop?
matRandom <- matrix(runif(n=600000), ncol=6)
## variant 1
system.time(test1 <- pmax(matRandom[,1], matRandom[,2], matRandom[,3],
matRandom[,4], matRandom[,5], matRandom[,6]))
User System verstrichen
0.01 0.00 0.01
## variant 2
system.time(test2 <- apply(matRandom, 1, max))
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0.56 0.00 0.56
## variant 3
system.time({
test3 <- matRandom[ ,1L]
## add a check that ncol(matrix) > 1L
for (i in 2:ncol(matRandom))
test3 <- pmax(test3, matRandom[ ,i])
})
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0.01 0.00 0.01
> all.equal(test1,test2)
[1] TRUE
> all.equal(test1,test3)
[1] TRUE
Regards,
Enrico
Am 12.10.2011 13:06, schrieb Wolfgang Wu:
I am having the following problem. I want to calculate the maximum of each row in a matrix. If I pass in the matrix split up by each column then this is no problem and works great. However I don't know how many columns I have in advance. In the example below I have 3 columns, but the number of columns is not fix. So how do I do this?
matRandom<- matrix(runif(n=30), ncol=3);
#Does not work
pmax(matRandom)
#Does work
pmax(matRandom[,1], matRandom[,2], matRandom[,3])
I am aware that I can do it with the apply function, but the calculation is time sensitive so fast execution is important.
#Apply might be too slow
matRandom<- matrix(runif(n=300000), ncol=3);
system.time(test<- pmax(matRandom[,1], matRandom[,2], matRandom[,3]))
system.time(test<- apply(matRandom, 1, max))
matRandom<- matrix(runif(n=300000), ncol=3); system.time(test<- pmax(matRandom[,1], matRandom[,2], matRandom[,3]))
user system elapsed
0.02 0.00 0.02
system.time(test<- apply(matRandom, 1, max))
user system elapsed
2.37 0.00 2.38 Thanks for your help. Regards. Wolfgang Wu
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Enrico Schumann Lucerne, Switzerland http://nmof.net/