Round with significant digits

Rounds towards the nearest number with N significant digits.

Description

This little function rounds a number (or the elements of a vector ot matrix) towards the nearest number with N significant digits.

Examples:
roundsd(0.012345,3) returns 0.0123
roundsd(12345,2) returns 12000
roundsd(12.345,4,'ceil') returns 12.35

This is a useful complement to Matlab's ROUND, ROUND10 and ROUNDN (Mapping toolbox), especially when dealing with data with a large variety of order of magnitudes.

I was about to upload this file when I found "sd_round.m" by Edward Zechmann (see aknowledgment), which has similar feature (and more). But, because my script is very different in coding (much much shorter), I decided to share it anyway.

Acknowledgements

Round To A Specified Number Of Significant Digits inspired this file.

• MATLAB release: MATLAB 6.5 (R13)

[Will]

Does not work in all cases. Try rounding 3.55 to 1 decimal place and you get 3.5 instead of 3.6

[Kamran Syed]

veru good

[Tobias Lamour]

a very useful extension to the usual round functions.

one small speed improvement can be achieved. Using find is very slow. one can use logical indexing just like this:
y(x==0) = 0;
it does the same job while much faster with lager arrays.
Thanks,
Tobi

[Walter de Vries]

Very nice simple and compact code.
Should be build into next Matlab versions.

[Milan]

 

[Nik F]

 

[K E]

 

[Brent Boehlert]

Much appreciated -- thanks.

[K E]

So useful that it should be built in to the Matlab round function, as it is in other languages

[Sunday]

 

[Forrest Brett]

 

[Oleg Komarov]

I think your submission deserves a much better overall rating.

[François Beauducel]

Thanks Oleg.
Yes, I will complete the "see also" function list in future updates.

1) you effectively need the "find" in Matlab versions < 7... and also single pipe for the OR test.
2) like you I have hesitated between "switch" and "feval". But the feval code is much shorter...

François.

[Oleg Komarov]

I would mention in the see also line the other rounding functions you use.

I never used matlab < 7 so I don't know if this applies:
1) no need to use find: y(find(x==0)) = 0;
2) I would use switch case instead of feval.

Oleg

[François Beauducel]

Thanks Daniel for your time. I submitted an updated version that corrects the zero-value behaviour, and I added some options for the rounding method.
About the mlint messages, I kept my original syntax which is voluntarily backward compatible (with Matlab versions < 7).

[Daniel Armyr]

I also noticed some mlint-messages that I fixed. The core of the code now looks like this:

if ~isnumeric(n) || numel(n) ~= 1 || n < 0 || mod(n,1) ~= 0
error('N argument must be a scalar positive integer.')
end

valuesZero = (x==0);
og = 10.^(floor(log10(abs(x)) - n + 1));
y = round(x./og).*og;
y(valuesZero) = 0;

[Daniel Armyr]

I just wrote one of these and was anout to upload it. But since you had allready done it, there is no point. This file would get a very high mark by me for several reasons:
1) Simple function, no bloated features
2) Error checking.
3) Well formated documentation.

Unfortunately, your script doesn't handle 0. That pulls down the mark significantly.