round function

older
Why is $ right associative instead...

Chatzianastassiou Achilleas

12 Feb 2006 12 Feb '06

4 p.m.

Hi all, I am trying to implement a function that finds the significant figure of a number to a specified point i.e. 2.55555 3 = 2.556. I have implemented something like: sig :: (RealFrac a, Integral b) => a -> Int -> a sig x y = round y However this doesn't work. Moreover at the Prelude when i type round 2.3333 2 i get an error. Any suggestions? Thanks, Skag55 _________________________________________________________________ Dont just search. Find. Check out the new MSN Search! http://search.msn.click-url.com/go/onm00200636ave/direct/01/

Show replies by date

Sebastian Sylvan

12 Feb 12 Feb

4:23 p.m.

On 2/12/06, Chatzianastassiou Achilleas wrote:

...

Hi all,

I am trying to implement a function that finds the significant figure of a number to a specified point i.e. 2.55555 3 = 2.556. I have implemented something like:

sig :: (RealFrac a, Integral b) => a -> Int -> a sig x y = round y

However this doesn't work. Moreover at the Prelude when i type round 2.3333 2 i get an error. Any suggestions?

Something like: myround n s = fromIntegral (round (n * factor)) / factor where factor = fromIntegral (10^s) Basically scaling it to bring the specified number of digits to the left of the decimal point, then rounding, then scaling back. /S -- Sebastian Sylvan +46(0)736-818655 UIN: 44640862

Chatzianastassiou Achilleas

5:34 p.m.

Thanks for the anwser Sebastian, this seems to work, however I am trying to implement something like Main> myfunction 123.456 2 120.0

...

From: Sebastian Sylvan Reply-To: sylvan@student.chalmers.se To: Chatzianastassiou Achilleas CC: haskell-cafe@haskell.org Subject: Re: [Haskell-cafe] round function Date: Sun, 12 Feb 2006 22:23:17 +0100

On 2/12/06, Chatzianastassiou Achilleas wrote:

...
Hi all,

I am trying to implement a function that finds the significant figure of a number to a specified point i.e. 2.55555 3 = 2.556. I have implemented something like:

sig :: (RealFrac a, Integral b) => a -> Int -> a sig x y = round y

However this doesn't work. Moreover at the Prelude when i type round 2.3333 2 i get an error. Any suggestions?

Something like:

myround n s = fromIntegral (round (n * factor)) / factor where factor = fromIntegral (10^s)

Basically scaling it to bring the specified number of digits to the left of the decimal point, then rounding, then scaling back.

/S

-- Sebastian Sylvan +46(0)736-818655 UIN: 44640862

_________________________________________________________________ FREE pop-up blocking with the new MSN Toolbar get it now! http://toolbar.msn.click-url.com/go/onm00200415ave/direct/01/

J. Garrett Morris

6:28 p.m.

I think the function you're looking for is: myRound n places = round (n / fromIntegral factor) * factor where factor = 10 ^ (places - 1) In this case, 10 ^ (places - 1) has integral type (either Int or Integer). I need it to be a fractional type to divide n by it, so I use fromIntegral to convert it. /g On 2/12/06, Chatzianastassiou Achilleas wrote:

...

Thanks for the anwser Sebastian,

this seems to work, however I am trying to implement something like Main> myfunction 123.456 2 120.0

...
From: Sebastian Sylvan Reply-To: sylvan@student.chalmers.se To: Chatzianastassiou Achilleas CC: haskell-cafe@haskell.org Subject: Re: [Haskell-cafe] round function Date: Sun, 12 Feb 2006 22:23:17 +0100

On 2/12/06, Chatzianastassiou Achilleas wrote:

...
Hi all,

I am trying to implement a function that finds the significant figure of a number to a specified point i.e. 2.55555 3 = 2.556. I have implemented something like:

sig :: (RealFrac a, Integral b) => a -> Int -> a sig x y = round y

However this doesn't work. Moreover at the Prelude when i type round 2.3333 2 i get an error. Any suggestions?

Something like:

myround n s = fromIntegral (round (n * factor)) / factor where factor = fromIntegral (10^s)

Basically scaling it to bring the specified number of digits to the left of the decimal point, then rounding, then scaling back.

/S

-- Sebastian Sylvan +46(0)736-818655 UIN: 44640862

_________________________________________________________________ FREE pop-up blocking with the new MSN Toolbar – get it now! http://toolbar.msn.click-url.com/go/onm00200415ave/direct/01/

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

-- We have lingered in the chambers of the sea By sea-girls wreathed with seaweed red and brown Till human voices wake us, and we drown.

Sebastian Sylvan

6:42 p.m.

On 2/13/06, J. Garrett Morris wrote:

...

I think the function you're looking for is:

myRound n places = round (n / fromIntegral factor) * factor where factor = 10 ^ (places - 1)

This gives: *Main> myRound 123123.123 2 123120 Whereas my (revised) version gives *Main> myround 123123.123 2 120000.0 I may be wrong, but I think it's this latter result he's looking for(?). /S -- Sebastian Sylvan +46(0)736-818655 UIN: 44640862

J. Garrett Morris

6:46 p.m.

Ah, okay. I misinterpreted.. I was thinking of round, just moving the other direction from the decimal point. /g On 2/12/06, Sebastian Sylvan wrote:

...

On 2/13/06, J. Garrett Morris wrote:

...
I think the function you're looking for is:

myRound n places = round (n / fromIntegral factor) * factor where factor = 10 ^ (places - 1)

This gives: *Main> myRound 123123.123 2 123120

Whereas my (revised) version gives

*Main> myround 123123.123 2 120000.0

I may be wrong, but I think it's this latter result he's looking for(?).

/S

-- Sebastian Sylvan +46(0)736-818655 UIN: 44640862

-- We have lingered in the chambers of the sea By sea-girls wreathed with seaweed red and brown Till human voices wake us, and we drown.

Chatzianastassiou Achilleas

6:48 p.m.

Ok, i have got it working. Thanks for the posts

...

From: "J. Garrett Morris" To: sylvan@student.chalmers.se CC: Chatzianastassiou Achilleas , haskell-cafe@haskell.org Subject: Re: [Haskell-cafe] round function Date: Sun, 12 Feb 2006 18:46:47 -0500

Ah, okay. I misinterpreted.. I was thinking of round, just moving the other direction from the decimal point.

/g

On 2/12/06, Sebastian Sylvan wrote:

...
On 2/13/06, J. Garrett Morris wrote:

...
I think the function you're looking for is:

myRound n places = round (n / fromIntegral factor) * factor where factor = 10 ^ (places - 1)

This gives: *Main> myRound 123123.123 2 123120

Whereas my (revised) version gives

*Main> myround 123123.123 2 120000.0

I may be wrong, but I think it's this latter result he's looking for(?).

/S

-- Sebastian Sylvan +46(0)736-818655 UIN: 44640862

-- We have lingered in the chambers of the sea By sea-girls wreathed with seaweed red and brown Till human voices wake us, and we drown.

_________________________________________________________________ Express yourself instantly with MSN Messenger! Download today - it's FREE! http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/

Chatzianastassiou Achilleas

6:43 p.m.

The myRound n places = round (n / fromIntegral factor) * factor where factor = 10 ^ (places - 1) seems to work for i.e. 2, but doesn't for 4, it returns 0. However the myround n s = fromIntegral (round (n * factor)) / factor where shift = s - (floor (logBase 10 n) + 1) factor = 10 ** fromIntegral shift works absolutely fine. Many thanks for the post. Skag

...

From: "J. Garrett Morris" To: Chatzianastassiou Achilleas CC: haskell-cafe@haskell.org Subject: Re: [Haskell-cafe] round function Date: Sun, 12 Feb 2006 18:28:40 -0500

I think the function you're looking for is:

myRound n places = round (n / fromIntegral factor) * factor where factor = 10 ^ (places - 1)

In this case, 10 ^ (places - 1) has integral type (either Int or Integer). I need it to be a fractional type to divide n by it, so I use fromIntegral to convert it.

/g

...
Thanks for the anwser Sebastian,

this seems to work, however I am trying to implement something like Main> myfunction 123.456 2 120.0

...
From: Sebastian Sylvan Reply-To: sylvan@student.chalmers.se To: Chatzianastassiou Achilleas CC: haskell-cafe@haskell.org Subject: Re: [Haskell-cafe] round function Date: Sun, 12 Feb 2006 22:23:17 +0100

On 2/12/06, Chatzianastassiou Achilleas wrote:

...
Hi all,

I am trying to implement a function that finds the significant

On 2/12/06, Chatzianastassiou Achilleas wrote: figure of

...
...
a

...
number to a specified point i.e. 2.55555 3 = 2.556. I have implemented something like:

sig :: (RealFrac a, Integral b) => a -> Int -> a sig x y = round y

However this doesn't work. Moreover at the Prelude when i type round 2.3333 2 i get an error. Any suggestions?

Something like:

myround n s = fromIntegral (round (n * factor)) / factor where factor = fromIntegral (10^s)

Basically scaling it to bring the specified number of digits to the left of the decimal point, then rounding, then scaling back.

/S

-- Sebastian Sylvan +46(0)736-818655 UIN: 44640862

_________________________________________________________________ FREE pop-up blocking with the new MSN Toolbar get it now! http://toolbar.msn.click-url.com/go/onm00200415ave/direct/01/

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

-- We have lingered in the chambers of the sea By sea-girls wreathed with seaweed red and brown Till human voices wake us, and we drown.

_________________________________________________________________ Dont just search. Find. Check out the new MSN Search! http://search.msn.click-url.com/go/onm00200636ave/direct/01/

Chatzianastassiou Achilleas

5:45 p.m.

In addition to my previous quote, I don't understand the user of fromIntegral At the prelude, when i type i.e. fromIntegral 4 it returns 4 Thanks

...

From: Sebastian Sylvan Reply-To: sylvan@student.chalmers.se To: Chatzianastassiou Achilleas CC: haskell-cafe@haskell.org Subject: Re: [Haskell-cafe] round function Date: Sun, 12 Feb 2006 22:23:17 +0100

On 2/12/06, Chatzianastassiou Achilleas wrote:

...
Hi all,

I am trying to implement a function that finds the significant figure of a number to a specified point i.e. 2.55555 3 = 2.556. I have implemented something like:

sig :: (RealFrac a, Integral b) => a -> Int -> a sig x y = round y

However this doesn't work. Moreover at the Prelude when i type round 2.3333 2 i get an error. Any suggestions?

Something like:

myround n s = fromIntegral (round (n * factor)) / factor where factor = fromIntegral (10^s)

Basically scaling it to bring the specified number of digits to the left of the decimal point, then rounding, then scaling back.

/S

-- Sebastian Sylvan +46(0)736-818655 UIN: 44640862

_________________________________________________________________ On the road to retirement? Check out MSN Life Events for advice on how to get there! http://lifeevents.msn.com/category.aspx?cid=Retirement

Sebastian Sylvan

6:35 p.m.

On 2/12/06, Chatzianastassiou Achilleas wrote:

...

In addition to my previous quote, I don't understand the user of fromIntegral At the prelude, when i type i.e. fromIntegral 4 it returns 4 Thanks

fromIntegral is overloaded. It will convert an Integral value (such as Int or Integer) to a numeric value (such as Double, Float, but also Integer and Int). When you type "fromIntegral 4" it will default the 4 to be an Integer, and it will default the result to be an integer as well. Try typing "fromIntegral 4 :: Double", indicating that the result should be a double, that will give you 4.0. I think this version will work better... Take the logarithm (in base 10) to find out how many digits to the left of the decimal point there is (and subract it from the "shift" amount). This can give negative shifts, so we use (**) instead of (^) since the latter can't deal with negative exponents. myround n s = fromIntegral (round (n * factor)) / factor where shift = s - (floor (logBase 10 n) + 1) factor = 10 ** fromIntegral shift -- Sebastian Sylvan +46(0)736-818655 UIN: 44640862

7038

Age (days ago)

7038

Last active (days ago)

List overview

Download

9 comments

3 participants

participants (3)

Chatzianastassiou Achilleas
J. Garrett Morris
Sebastian Sylvan

round function

Chatzianastassiou Achilleas

Sebastian Sylvan

Chatzianastassiou Achilleas

J. Garrett Morris

Sebastian Sylvan

J. Garrett Morris

Chatzianastassiou Achilleas

Chatzianastassiou Achilleas

Chatzianastassiou Achilleas

Sebastian Sylvan

tags

participants (3)