How to round up price to multiple of 5?

[poutses]

I've tried other the ciel and the RoundUp functions and can't seem to get this right. Suppose price=3653.69829

When I use

ceil(price)

It just rounds up to the nearest integer and displays 3,654. Adding any other parameters to the ceil function gives an error.

When I use

RoundUp(price, 5);

It just displays 3,653.6983

When I use

RoundUp(price, -1);

It displays 3,660, not 3,655

Anyone have an idea on how to get it to round up to 3,655?

 

[SleepyZ]

I've tried other the ciel and the RoundUp functions and can't seem to get this right. Suppose price=3653.69829

When I use

ceil(price)

It just rounds up to the nearest integer and displays 3,654. Adding any other parameters to the ceil function gives an error.

When I use

RoundUp(price, 5);

It just displays 3,653.6983

When I use

RoundUp(price, -1);

It displays 3,660, not 3,655

Anyone have an idea on how to get it to round up to 3,655?

Try

plot  price = 3653.69829;
AddLabel(1, Round((price / 5), 0) * 5);

 

[poutses]

Try

So that works for that specific example, but it doesn't work if the number changes to 3727.49. It then just rounds it down to 3725 instead of up to 3730.

 

[SleepyZ]

So that works for that specific example, but it doesn't work if the number changes to 3727.49. It then just rounds it down to 3725 instead of up to 3730.

So you don't want the nearest value ending in 5 which is what I thought you wanted. Since I am not a math expert, who can do this better, this seems to work for both of your requests.

input  price = 3727.49;
#AddLabel(1, Round((roundup(price,0) / 5), 0) * 5);

AddLabel(1, if Round((price / 5), 0) * 5 < price
            then Round(price / 10, 0) * 10
            else Round((price / 5), 0) * 5 );

 

[mashume]

Please read up on these functions:
https://tlc.thinkorswim.com/center/reference/thinkScript/Functions/Math---Trig/Ceil
https://tlc.thinkorswim.com/center/reference/thinkScript/Functions/Math---Trig/Floor

and these three:
https://tlc.thinkorswim.com/center/reference/thinkScript/Functions/Math---Trig/Round
https://tlc.thinkorswim.com/center/reference/thinkScript/Functions/Math---Trig/RoundDown
https://tlc.thinkorswim.com/center/reference/thinkScript/Functions/Math---Trig/RoundUp

There are many ways to 'round' numbers. And then there is "bankers" rounding:
https://en.wiktionary.org/wiki/bankers'_rounding

Each has an application that it is best suited for. None of them are really interchangeable.

from your example, 3727.49 should round down to 3725.
you can try roundUp to get your preferred answer of 3730, but asking for round to get you that answer will not work.

@SleepyZ 's answer :

AddLabel(1, Round((price / 5), 0) * 5);

does provide the best way to round to the nearest multiple of 5.

Perhaps it is illustrative to see some results of different rounding:

AddLabel(1, Round((price / 5), 0) * 5);
--> 3725

AddLabel(1, RoundDown((price / 5), 0) * 5);
--> 3725

AddLabel(1, RoundUp((price / 5), 0) * 5);
--> 3730

AddLabel(yes, Round(price, 2 ));
--> 3727.49

AddLabel(yes, Round(price, 1 ));
--> 3727.5

AddLabel(yes, Round(price, 0 ));
--> 3727

AddLabel(yes, Round(price, -1 ));
--> 3730

AddLabel(yes, Round(price, -2 ));
--> 3700

Your example, rounding 27.49 up to 30 by thinking that the .49 rounds up to .5 and then .5 rounds up again to 30 is called double rounding, and is not generally employed by algorithms. The algorithm looks at the 27.4 and decides that .4 rounds down, and so 27.49 rounds down to 27 rather than up to 28 and therefore your request to get to the nearest 5 is based on 27 (which goes down) rather than 28 (which would go up).

This is probably a lot longer an answer than you wanted, but I spend a lot of time thinking about how different programs and databases work with rounding. And don't ask me to explain MS Excel does it. I don't want to think about it!!! ;-)

-mashume

 

[poutses]

Thanks @mashume for the detailed explanation. It got me thinking a bit more and I was able to figure out a workaround in my script using your suggestions and @SleepyZ's original solution

 

[halcyonguy]

So that works for that specific example, but it doesn't work if the number changes to 3727.49. It then just rounds it down to 3725 instead of up to 3730.

here is an example code to show 3 type of integer rounding, based on some devisor number
you want the rndup formula

input price = 3727.49;
input round_devisor = 5;

def rnd = floor((price + (round_devisor/2)) / round_devisor) * round_devisor;
def rndup = floor((price + round_devisor) / round_devisor) * round_devisor;
def rnddown = floor(price / round_devisor) * round_devisor;

addlabel(1, "orig " + price, color.white);
addlabel(1, "rounding devisor " + round_devisor, color.white);

addlabel(1, "round " + rnd, color.yellow);
addlabel(1, "round up " + rndup, color.green);
addlabel(1, "round down " + rnddown, color.red);
#

----------------------------------

@mashume
thanks for typing out those rounding examples. i added them to my collection of snippets.
there is a typo on the first one , should be 3725

AddLabel(1, Round((price / 5), 0) * 5);
--> 3730

 

[mashume]

@mashume
thanks for typing out those rounding examples. i added them to my collection of snippets.
there is a typo on the first one , should be 3725

AddLabel(1, Round((price / 5), 0) * 5);
--> 3730

Ugh. Typos. Fixed the post above. Thanks for pointing it out. Happy the examples are worth adding to your snippets collection.

-mashume