round digits

Community Support
1

Hi,

I would like to round the digits of a number column to a certain
precision, e.g. two decimal places (44.678 => 44.68). I tried to use
floor function but couldn’t get it to work.

Please advise and thanks in advance.

Nick

2

On Oct 1, 2009, at 10:31 PM, Ninja Li wrote:

> I would like to round the digits of a number column to a certain
> precision, e.g. two decimal places (44.678 => 44.68). I tried to use
> floor function but couldn’t get it to work.

floor isn’t round, it’s floor–it truncates. depending on exactly what
you’re doing, you may want to set the precision with P, or you may
want to use .Q.fmt:

q)P 4
q)44.678
44.68
q).Q.fmt[5;2;44.678]
“44.68”

3

Aaron, Thanks for your help. Could you please tell me where I can find anydocumentation on this function? I have googled but to no avail. NickOn Oct 1, 11:10?am, Aaron Davies <aaron.dav…> wrote:> On Oct 1, 2009, at 10:31 PM, Ninja Li wrote:>> > ? I would like to round the digits of a number column to a certain> > precision, e.g. two decimal places (44.678 => 44.68). I tried to use> > floor function but couldn’t get it to work.>> floor isn’t round, it’s floor–it truncates. depending on exactly what ?> you’re doing, you may want to set the precision with \P, or you may ?> want to use .Q.fmt:>> q)\P 4> q)44.678> 44.68> q).Q.fmt[5;2;44.678]> “44.68”</aaron.dav…>

4

X-Mailer: Apple Mail (2.936)

https://code.kx.com/trac/wiki/DotQ/DotQDotfmt

login is anonymous/anonymous

5

Hi, if there a way to round it more than 2 digit? Say 4 digit / 6 digit? I’ve just check the document but doesn’t aware it mentioned it

6

<o:p> </o:p>

q)round:{[d;n]  (“j”$n*d) % d:xexp[10]d  }     <o:p></o:p>

q)round[3]12.12345                            <o:p></o:p>

12.123                                         <o:p></o:p>

q)round[3]12.12355                            <o:p></o:p>

12.124                                         <o:p></o:p>

<o:p> </o:p>

HTH,<o:p></o:p>

<o:p> </o:p>

Kim<o:p></o:p>

<o:p> </o:p>

Von: personal-kdbplus@googlegroups.com [mailto:personal-kdbplus@googlegroups.com] Im Auftrag von Carfield Yim
Gesendet: Dienstag, 5. Januar 2016 10:20
An: Kdb+ Personal Developers
Betreff: Re: [personal kdb+] Re: round digits<o:p></o:p>

<o:p> </o:p>

Hi, if there a way to round it more than 2 digit? Say 4 digit / 6 digit? I’ve just check the document but doesn’t aware it mentioned it

7

it is often useful to round to values other than powers of 10:

rnd:{x*“j”$y%x}

q).01 .02 .05 rnd: 10?1f
0.02 0.36 0.03 0.69 0.64 0.04 0.9 0.79 0.2 0.78
0.02 0.36 0.02 0.68 0.64 0.04 0.9 0.8  0.2 0.78
0    0.35 0.05 0.7  0.65 0.05 0.9 0.8  0.2 0.8

q)00:01 00:05 00:10 rnd: 10?1u
00:18 00:24 00:51 00:58 00:52 00:17 00:54 00:27 00:44 00:15
00:20 00:25 00:50 01:00 00:50 00:15 00:55 00:25 00:45 00:15
00:20 00:20 00:50 01:00 00:50 00:20 00:50 00:30 00:40 00:20

scientific notation can be used to retain the ability to compactly specify the number of decimals:

q)rnd[1e-5] 5?1f
0.49478 0.86656 0.6415 0.90827 0.97961

?

8

there’s a builtin string rounder that’s used by .Q.fmt

q)3 .Q.f’12.12345 12.12355
“12.123”
“12.124”
q)

you can use “get” (or “F”$, etc.) on the result if you want it back as
a number, not a string

there’s also xbar, but that effectively uses floor, not rounding, and
it has some type issues