Mathematica Asked by mrz on April 1, 2021
How can I improve significantly the speed of the following code?
nmax = 10000000;
r = Range[nmax];
res = ({#, #^2, If[Mod[#, 2] == 0, "even", "odd"]} & /@ r); // AbsoluteTiming
{15.3145, Null}
res = Transpose[{r, r^2, Mod[r, 2]}];
This is about 50 times faster than the original code on my machine and contains the same information. I replaced the strings by integers (0
or 1
), because that allows one to use vectorization and packed arrays.
If you insist on the strings, you can try
res = Transpose[{r, r^2, {"odd", "even"}[[Mod[r, 2, 1]]]}];
which is still 5 times faster than the original code.
But this also shows drastically that transposing an unpackedable array can be very expensive. (Run the code without Transpose
and compare the runtime.)
Correct answer by Henrik Schumacher on April 1, 2021
Another trick, not so efficient.
nmax = 1000;
r = Range[nmax];
f[x_] := {x, x^2, If[EvenQ@x, "even", "odd"]};
SetAttributes[f, Listable];
res1 = (f@r); // AbsoluteTiming
{0.0026543, Null}
This is the origin code.
{0.003949, Null}
res1 == res2
True
Answered by wuyudi on April 1, 2021
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