Decimal.Round lunacy

[Rob Oldfield]

From the documentation about Decimal.Round.. ..

"When d is exactly halfway between two rounded values, the result is the
rounded value that has an even digit in the far right decimal position. For
example, when rounded to two decimals, the value 2.345 becomes 2.34 and the
value 2.355 becomes 2.36. This process is known as rounding toward even, or
rounding to nearest."

I'd have to disagree. I'd go for something more like "This process is known
is arbitrarily ignoring a de facto standard." Does anyone have a sensible
method of returning the correct rounded value i.e. without resorting to
decimal.round(x +0.00000001,2)

And has anyone got any justification for this ludicrousness?

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[Rob Oldfield]

....and something else I didn't think of in my previous answer....

The vast majority of bankers thoughout the world are using Excel. The round
function in Excel works on the 'round halves up' method. Either they all
know about the difference between their hand-crafted figures and the central
office system and they've given themselves a way around it, or there are a
lot of pennies going missing somewhere.

Next question: can you think of a way of funnelling all these pennies into
an account that I'll set up tomorrow?

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"Jon Skeet [C# MVP]" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@msnews.micros oft.com...

Rob Oldfield <r$ob@oldfi$eld 100.freese$rve. c$o.uk> wrote:

I repeat. It's lunacy. It might be a good idea, but the fact is that
NOBODY ACTUALLY DOES IT THIS WAY.

Well, that might be an exaggeration, but very few people.

I suspect that decimal is generally intended for financial
applications, and given that the name is "banker's rounding" my guess
is that it's not uncommon in that sector. I don't personally have a lot
of experience with the financial sector - do you?

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Colin Young]

This isn't going to solve the problem for you, but it does provide
justification: http://tinyurl.com/vv4v

Colin

"Rob Oldfield" <r$ob@oldfi$eld 100.freese$rve. c$o.uk> wrote in message
news:OD******** ******@TK2MSFTN GP12.phx.gbl...

From the documentation about Decimal.Round.. ..

"When d is exactly halfway between two rounded values, the result is the
rounded value that has an even digit in the far right decimal position. For example, when rounded to two decimals, the value 2.345 becomes 2.34 and the value 2.355 becomes 2.36. This process is known as rounding toward even, or rounding to nearest."

I'd have to disagree. I'd go for something more like "This process is known is arbitrarily ignoring a de facto standard." Does anyone have a sensible
method of returning the correct rounded value i.e. without resorting to
decimal.round(x +0.00000001,2)

And has anyone got any justification for this ludicrousness?

--
For real reply address, lose the cash
www.realuk.co.uk

[Rob Oldfield]

Thanks for that. I get the justification and it does indeed make sense (in
much the same way that the optimal keyboard layout as opposed to QWERTY),
but the problem is if nobody in the real world actually uses it. As I've
said elsewhere in this thread, it may be that US bankers do, but UK ones
certainly don't.

I'd also say that it's not the way that the function works that is the
problem but, as Jon and William point out, that there isn't a sensibly
accessible method of choosing what method to use.

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"Colin Young" <[e-mail] > wrote in message
news:ON******** ******@TK2MSFTN GP09.phx.gbl...

This isn't going to solve the problem for you, but it does provide
justification: http://tinyurl.com/vv4v

Colin

"Rob Oldfield" <r$ob@oldfi$eld 100.freese$rve. c$o.uk> wrote in message
news:OD******** ******@TK2MSFTN GP12.phx.gbl...

From the documentation about Decimal.Round.. ..

"When d is exactly halfway between two rounded values, the result is the
rounded value that has an even digit in the far right decimal position.

For

example, when rounded to two decimals, the value 2.345 becomes 2.34 and

the

value 2.355 becomes 2.36. This process is known as rounding toward even,

or

rounding to nearest."

I'd have to disagree. I'd go for something more like "This process is

known

is arbitrarily ignoring a de facto standard." Does anyone have a sensible method of returning the correct rounded value i.e. without resorting to
decimal.round(x +0.00000001,2)

And has anyone got any justification for this ludicrousness?

--
For real reply address, lose the cash
www.realuk.co.uk

[Kevin Gale]

"Rob Oldfield" <r$ob@oldfi$eld 100.freese$rve. c$o.uk> wrote in message

And has anyone got any justification for this ludicrousness?

It's not any more ludicrous than deciding that x.5 always rounds up when
it is in fact equally close to the value below it. In fact it is statistically
much
better to sometimes round up and sometimes round down in that case.

Both methods have their place.
I like Jon's idea. There should be an enumeration of rounding types.

-- Kevin Gale

[Matthew W. Jackson]

I always found it VERY odd that Excel used Arithmetic rounding (.5 rounds
up), where as VBA (which is integrated into Excel), and therefore
VisualBasic 6, use Banker's rounding.

If you think Banker's rounding is "lunacy", then you probably have never
done any work in statistics. Using arithmetic rounding is asymmetric, and
can skew data. Very bad....

This page explains rounding and how Excel rounds in various cases.
http://support.microsoft.com/default...b;EN-US;196652

Read down on the page, and it describes the reasoning. Here's an excerpt:

"When you add rounded values together, always rounding .5 in the same
direction results in a bias that grows with the more numbers you add
together. One way to minimize the bias is with banker's rounding.

Banker's rounding rounds .5 up sometimes and down sometimes. The convention
is to round to the nearest even number, so that both 1.5 and 2.5 round to 2,
and 3.5 and 4.5 both round to 4. Banker's rounding is symmetric."

In fact, in any statistics project I did in college, we were required to use
either Banker's rounding or Random rounding. I was annoyed to find that I
had to implement my own rounding function in Excel to do Banker's rounding.
Go figure.

--Matthew W. Jackson

[Rob Oldfield]

For what it's worth, I never meant to imply that I thought the method of
banker's rounding was lunatic. What I _did_ mean was that Microsoft's
decision to arbitratily impose one method, and to choose a non-standard one,
was lunatic.

--
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"Matthew W. Jackson" <th************ ********@NOSPAM .NOSPAM> wrote in message
news:Oo******** ******@TK2MSFTN GP11.phx.gbl...

I always found it VERY odd that Excel used Arithmetic rounding (.5 rounds
up), where as VBA (which is integrated into Excel), and therefore
VisualBasic 6, use Banker's rounding.

If you think Banker's rounding is "lunacy", then you probably have never
done any work in statistics. Using arithmetic rounding is asymmetric, and
can skew data. Very bad....

This page explains rounding and how Excel rounds in various cases.
http://support.microsoft.com/default...b;EN-US;196652

Read down on the page, and it describes the reasoning. Here's an excerpt:

"When you add rounded values together, always rounding .5 in the same
direction results in a bias that grows with the more numbers you add
together. One way to minimize the bias is with banker's rounding.

Banker's rounding rounds .5 up sometimes and down sometimes. The convention is to round to the nearest even number, so that both 1.5 and 2.5 round to 2, and 3.5 and 4.5 both round to 4. Banker's rounding is symmetric."

In fact, in any statistics project I did in college, we were required to use either Banker's rounding or Random rounding. I was annoyed to find that I
had to implement my own rounding function in Excel to do Banker's rounding. Go figure.

--Matthew W. Jackson

[Rob Oldfield]

Always rounding up may be ludicrous, but the point is that it's a standard
ludicrous.

--
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"Kevin Gale" <kg***@PLEASE-DELETEprintcafe .com> wrote in message
news:10******** *****@mail1.seg net.com...

"Rob Oldfield" <r$ob@oldfi$eld 100.freese$rve. c$o.uk> wrote in message

And has anyone got any justification for this ludicrousness?
It's not any more ludicrous than deciding that x.5 always rounds up when
it is in fact equally close to the value below it. In fact it is

statistically much
better to sometimes round up and sometimes round down in that case.

Both methods have their place.
I like Jon's idea. There should be an enumeration of rounding types.

-- Kevin Gale

[Kevin Gale]

"Rob Oldfield" <rob@oldfield10 0_wow_freeserve _yikes_co_incre dible!_uk> wrote in
message news:uV******** ******@TK2MSFTN GP11.phx.gbl...

Always rounding up may be ludicrous, but the point is that it's a standard
ludicrous.

Standard for who? Microsoft does it both ways in different products and Borland
uses banker's rounding in most of it's products but has a few exceptions. I'm
positive that a little research would come up the lots of products that do it
one way and lots the other. Seems like the problem is that there is no standard
(although I'm told that the IEEE 754 floating-point standard does specify
banker's rounding).

I agree with you in the sense that it should be a standard one way or the other.
Having it change from one product to another is just asking for trouble.

-- Kevin