Bioequivalence and Bioavailability Forum

Speeed! [Two-Stage / GS Designs]

posted by Helmut  – Vienna, Austria, 2015-02-21 02:11 (3345 d 10:30 ago) – Posting: # 14481
Views: 11,401

Hi ElMaestro,

❝ ❝ for(j in seq_along(run)) v1 <- c(v1, rnorm(1, mean=0, sd=1))

❝

❝ This is a funny way to do it. There will be constant memory re-allocation of the vector this way. I guess that's what takes the time.

Exactly. That’s really stupid (see the R Inferno Circle 2). Detlew cured me.

❝ The idea is (and pardon me for going from a for loop to a while loop; this is just because I don't know of a way to make a for loop increase by more than one per iteration, but I am sure you can do that):

I have learned that one never ever should try to manipulate the counter of a for-loop.

runs <- 1e7
ptm  <- proc.time()
i    <- 1
while (i <= runs) {
  # Do.Something(i)
  i <- i+1
}
t1   <- proc.time()-ptm
ptm  <- proc.time()
i    <- 1
while (i <= runs) {
  # Do.Something(i)
  # Do.Something(i+1)
  i <- i+2
}
t2   <- proc.time()-ptm
cat("\n",
"simple :", t1[3], "seconds\n",
"partial:", t2[3], "seconds\n")

 simple : 5.07 seconds
 partial: 2.55 seconds

But: Quite often the number of iterations is not known beforehand (here it must be even) and the time-consuming part is the Do.Something().
Reminds me on my first Pascal-lessons almost 40 years ago.

Instead of    better use
y := 2*x;     y := x+x;   (addition faster than multiplication)
y := x/2;     y := 0.5*x; (multiplication faster than division)

Not kiddin’.

—
Dif-tor heh smusma 🖖🏼 Довге життя Україна! 
Helmut Schütz


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Complete thread:

• Gimmick & survey Helmut 2015-02-20 01:47 
  • Gimmick & survey nobody 2015-02-20 08:25
    • Gimmick & survey Helmut 2015-02-20 13:01
      • Gimmick & survey nobody 2015-02-20 14:18
        • Speeed! Helmut 2015-02-20 15:38
          • Speeed! nobody 2015-02-20 16:37
            • Speeed! Helmut 2015-02-20 16:58
              • Speeed! nobody 2015-02-20 17:01
          • Speeed! ElMaestro 2015-02-20 23:48
            • Speeed!Helmut 2015-02-21 01:11
              • Unrolled example ElMaestro 2015-02-21 01:32
                • Unrolled example Helmut 2015-02-21 01:50
                  • Unrolled example ElMaestro 2015-02-21 02:27
                    • Increasing vector & another example Helmut 2015-02-21 13:13
              • Speeed! nobody 2015-02-21 21:02