How to avoid If statement?

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JFz
JFz 2015-8-19
评论： JFz 2015-8-20
Hi,
I have a few lines of code like this:
if(volTbl.ReturnType(k) == 1)
logR = diff(log(abs(newtable.price)));
else
logR = diff(newtable.price);
end
I would like to avoide the if statement because the tables are large and the calculation is intensive. How to do that? Thanks a lot.
Jennifer
  2 个评论
Image Analyst
Image Analyst 2015-8-19
How large? Like hundreds of millions of elements?
And it's not the "if" that's taking up the time, it's the diff(), and log(). Is this code in a loop over many millions of iterations? Or is it just a one time calculation?
JFz
JFz 2015-8-20
Thanks. yes, you are right. It is indeed in a large for loop.

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回答（1 个）

Walter Roberson
Walter Roberson 2015-8-19
selectfun = @(cond, tf_funs, x) tf_funs{cond+1}(x);
logR = diff( selectfun(volTbl.ReturnType(k) == 1, {@(x) log(abs(x)), @(x) x}, newtable.price) );
This does not use "if", but I suspect it will be slower than if you used "if".
To get much performance improvement you would need to be writing to a different result location for each "k", such as if the statement were logR(k,:) = ... and you would need a different input location for each, such as newtable(k).price, and you would need to be doing a whole series of "k" values. But when your input is always the same and your output is always the same and you are only doing one "k" value, then it is difficult to get faster than "if".

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