Skip to content

object size of a matrix and a list

2 messages · Kyeongmi Cheon, jim holtman

Kyeongmi Cheon
# 
Hello,
My program calculates several variables at each iteration and some of them are

integers and the rest are numeric. When I save them into a matrix, all of them

are of numeric type, of course.

I'm trying to find a way to save time/memory of my program and I was thinking

that it might help to force some variables to be of integer type and the other

columns numeric type.

But when I actually tried it, I found it contrary. A list that has mixtures of

integers and doubles are larger in size than a matrix that has only doubles. Do

lists always take up more space than matrices if they have the same/similar

variables? I just want to know it for the sake of efficiency. Thank
you for your time.
Kyeongmi


My short test program is here:


   #matrix
   beta.mat <- matrix(0,nr=5, nc=2)
   for (i in 1:5){
      beta.mat[i,] <- c(i,i*10.0)
   }

   #list
   gamma.mat <- list()
   for (i in 1:5){
      gamma.mat$aa[i] <- i
      gamma.mat$bb[i] <- i*10.0
   }

   object.size(beta.mat) #240
   object.size(gamma.mat) #312
jim holtman
# 
You were doing for a small size where the overhead masked the gains.
Here a larger case where you can see the differences:
[1] 800112
[1] 600408
List of 2
 $ a: int [1:500, 1:100] 1 1 1 1 1 1 1 1 1 1 ...
 $ b: num [1:500, 1:100] 1 1 1 1 1 1 1 1 1 1 ...
How big do you expect your data items to get?  No need to try to
optimize if they are not large (e.g., taking up 10% of your available
memory).
On Wed, Mar 18, 2009 at 10:14 PM, Kyeongmi Cheon <katie.cheon at gmail.com> wrote: