chopDigit

Remove unwanted digits from numbers.

Description

This method provides a means to specify how many digits of precision to give to a number. For instnace if you have number which is 19.2 and another calculated number that is 19.2000000001 that are suppose to be equal you can just chop the digits for the 19.2000000001 to one digit of precision and then the two numbers will be equal.

• MATLAB release: MATLAB 6.1 (R12.1)

[Jos jnvdg @ arcor DOT de]

There are numerous better and faster ways to do this!
e.g. fix(N * (10^P)) / (10^P) with N the number and P the precision.

[Charles Zane]

It might not be the fastest or best way to do it. But it shows outside of the box thinking! "A" for effort. What with processors being upwards of 3.2 GHz I don't think speed is an issue.

[Toby Fernsler]

Both ChopDigit.m nor Jos' suggested solution assume the data is of the form #.###. So for example if you want to round 582.34 to 4 significant digits (582.3), these approaches would instead yield 582.3400; 4 decimal places of precision. I have not found a decent solution, a comment in Support mentions the program CHOP, but I can't find it. The symbolic toolboxs can do this many ways, but they're too slow for my needs.

[Ranganathan Sridharan]

Good Job! Exactly met my requirements.

[Andreas Zöllner]

I would propose the following:
function result = significant(x, n)
% significant(x, n) rounds number x to n number of significant figures

s = floor(log10(abs(x)));
shift = 10^(n-1);
mant = round(x*shift/(10^s)) / shift;
result = mant * 10^s;

[Matthew McMahon]

Not bad, but Andreas' proposal works much better for negative numbers.