[Rd] extracting rows from a data frame by looping over the row names: performance issues

[Herve Pages]

Herve Pages wrote:
...
> But if, instead of the above, I do this:
> 
>   > for (i in nrow(dat)) { row <- sapply(dat, function(col) col[i]) }

Should have been:

  > for (i in 1:nrow(dat)) { row <- sapply(dat, function(col) col[i]) }

> 
> then it's 20 times faster!!
> 
>   > system.time(for (i in 1:100) { row <- sapply(dat, function(col) col[i]) })
>      user  system elapsed
>     0.576   0.096   0.673

...

Cheers,
H.