Speed Tips
- To: mathgroup at smc.vnet.net
- Subject: [mg39601] Speed Tips
- From: "Ersek, Ted R" <ErsekTR at navair.navy.mil>
- Date: Tue, 25 Feb 2003 02:57:28 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
I have a tip (or a few tips) that can slightly improve the speed of
programs. I figured this is worth mentioning because I notice that even
some experts don't take advantage of this.
First[expr] is faster than expr[[1]]
Last[expr] is faster than expr[[-1]]
Rest[expr] is faster than Drop[expr,1]
Head[expr] is faster than expr[[0]]
Apparently First, Last, Rest, Head are more efficient because they don't
need to see which parts to return, and I am sure these functions were
created for this very reason. In general one should always use the form
that requires the minimum work for the kernel. So for example:
Don't use Table[expr,{i,imax}] when Table[expr,{imax}] will work.
Don't use Do[expr,{i,imax}] when Do[expr,{imax}] will work.
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Regards,
Ted Ersek
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