Equivalent to rowMeans() for min()

Question

I have seen this question being asked multiple times on the R mailing list, but still could not find a satisfactory answer.

Suppose I a matrix m

m <- matrix(rnorm(10000000), ncol=10)  

I can get the mean of each row by:

system.time(rowMeans(m))      user  system elapsed      0.100   0.000   0.097 

But obtaining the minimum value of each row by

system.time(apply(m,1,min))      user  system elapsed     16.157   0.400  17.029 

takes more than 100 times as long, is there a way to speed this up?

Answer 1

You could use pmin, but you would have to get each column of your matrix into a separate vector. One way to do that is to convert it to a data.frame then call pmin via do.call (since data.frames are lists).

system.time(do.call(pmin, as.data.frame(m))) #    user  system elapsed  #   0.940   0.000   0.949  system.time(apply(m,1,min)) #    user  system elapsed  #   16.84    0.00   16.95