Fast fingers. Had to change the test:
> vlarge <- c(numeric(20),1:20)
> system.time(
+ for (i in 1:30000) {
+ which.min(!(vlarge != 0))}) # test changed
user system elapsed
0.35 0.00 0.42
>
> #Method 2:
> system.time(
+ for (i in 1:30000) {
+ for (i in 1:40) {
+ if (vlarge[i] != 0) {
+ break
+ }
+ }})
user system elapsed
2.43 0.00 2.78
>
On Tue, Sep 15, 2009 at 7:51 PM, Bryan Keller <bskel...@wisc.edu> wrote:
> Anyone familiar with a quicker method to find the position of the first
> non-zero element of a vector?
>
> #The first way:
> print(min(which(vector != 0)))
>
> #The second way:
> for(i in 1:length(vector)) {
> if (vector[i] != 0) {
> print(i)
> break
> }
> }
>
> The first way seems to be faster for larger vectors (or when the first
> non-zero is deeper in)...
>
> vlarge <- c(numeric(20),1:20)
>
> #Method 1:
> system.time(
> for (i in 1:30000) {
> min(which(vlarge != 0))})
> # user system elapsed
> # 0.49 0.00 0.48
>
> #Method 2:
> system.time(
> for (i in 1:30000) {
> for (i in 1:40) {
> if (vlarge[i] != 0) {
> break
> }
> }})
> # user system elapsed
> # 0.99 0.02 0.99
>
> --------------------------------------------------
> The second way seems to be faster for smaller vectors (or when the first
> non-zero is closer to the front)...
>
> vsmall <- c(numeric(5),1:5)
>
> #Method 1:
> system.time(
> for (i in 1:30000) {
> min(which(vsmall != 0))})
> # user system elapsed
> # 0.41 0.00 0.42
>
> #Method 2:
> system.time(
> for (i in 1:30000) {
> for (i in 1:10) {
> if (vsmall[i] != 0) {
> break
> }
> }})
> # user system elapsed
> # 0.31 0.02 0.31
>
> Or, might the fastest way be to choose between the two methods on-the-fly
> based on length of the vector, etc.?
>
> Bryan
>
>
> -------------
> Bryan Keller, Doctoral Student/Project Assistant
> Educational Psychology - Quantitative Methods
> The University of Wisconsin - Madison
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
--
Jim Holtman
Cincinnati, OH
+1 513 646 9390
What is the problem that you are trying to solve?
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