Fast access to N-th figure in number

Slawa,

For a number n, how about:

mod(abs(truncate(n*1000)) 10)

Regards,

Andrew.

Many thanks for the help. And unless multiplication and division operations are not the slowest for performance by processors or my knowledge have become outdated :) ?

Best regards

Slawa 

Slawa,

I doubt this would end up being a performance bottleneck in any practical code you write. Multiplication is pretty fast compared with many other higher level operations (such as list construction and garbage collection). You could also use something like this:

 atoi(substring(index(sprintf(nil "%.9f" n) ".") 4 1))

I used 9 digits in the sprintf because if you only use 3, it will round the 3rd digit - depends of course what you want. I'd be really surprised if this was faster though.

I did a quick check (using the SKILL profiler) and if I run 10 million calls to the above two different statements, the mod() version takes 15 seconds (5 of which is in gc, 4 in truncate, and only 1 in times), whereas the string-based approach takes 30 seconds, 15 of which is in sprintf, and 10 in substring and index.

15 seconds for 10 million calls is not exactly bad... and as I said, I'd expect building a list with this number of items would almost certainly take longer.

Regards,

Andrew.

 Well but how to be in that case for example?

x=514.540
x_mod=mod (abs (truncate (x1*1000)) 10)

x_mod == 9 but not 0

Sorry I already has understood itself. How to delete a post?

 Best regards

Slawa 

Hi Slawa,

Rounding errors again. The x*1000 ends up being slightly smaller than 514540, so truncate ends up being 514539. Adding a small epsilon would solve this:

 x_mod=mod(truncate(abs(x*1000)+1e-6) 10)

I changed the order of the truncate and abs to ensure that the epsilon adds upwards for negative numbers.

Regards,

Andrew.

    Thanks Andrew. A variant with addition an epsilon I think it is equivalent to replacement truncate on round in a case when 4 sign after a comma it is guaranteed it is equal 0

Best regards

Slawa 

I didn't suggest using round() instead because if you had  514.5405 it would give 1 as the 3rd digit after the point. Now it maybe that's what you actually want - if it is, then use round() rather than truncate().

Regards,

Andrew.