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MathGroup Archive 2001

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Re: How can I transform the number of 123.456 into "123.456"?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg26585] Re: [mg26515] How can I transform the number of 123.456 into "123.456"?
  • From: Erich Mueller <emuelle1 at uiuc.edu>
  • Date: Tue, 9 Jan 2001 01:51:59 -0500 (EST)
  • Organization: University of Illinois at Urbana-Champaign
  • References: <200101010732.CAA09656@smc.vnet.net> <92uqmk$drv@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

A much simpler solution to getting more significant figures in your
string:

ToString[InputForm[345.89087]]

Other formats can be used for more sophisticated outputs.

Erich



On 3 Jan 2001, Tomas Garza wrote:

> I see your problem. If you have a real number, a simple ToString[] will not
> work the way you want, since there will be a roundoff at the end:
> 
> In[1]:=
> ToString[345.89087]
> Out[1]=
> "345.891"
> 
> Then I suggest the following approach. Take first
> 
> In[2]:=
> a = RealDigits[345.89087]
> Out[2]=
> {{3, 4, 5, 8, 9, 0, 8, 7, 0, 0, 0, 0, 0, 0, 0, 0}, 3}
> 
> Notice that the last element gives the number of digits that are to the left
> of the decimal point, 3 in this example. Then search for the significant
> digits, i.e. get rid of the sequence of zeros (if any) at the end. Define a
> function zeroAtTheEnd:
> 
> In[3]:=
> zeroAtTheEnd[y_] := y /. {x__, 0} -> {x}
> 
> which gets rid of the ending zero, if any. Nest this function until the
> result no longer changes, i.e., there is no zero at the end. To do this, we
> use FixedPoint[]:
> 
> In[4]:=
> b = FixedPoint[zeroAtTheEnd, a[[1]]]
> Out[4]=
> {3, 4, 5, 8, 9, 0, 8, 7}
> 
> Finally,
> 
> In[5]:=
> ToString[FromDigits[Take[b, a[[2]]]]] <> "." <>
>   ToString[FromDigits[Take[b, -Length[b] + a[[2]]]]]
> Out[5]=
> "345.89087"
> 
> **However**, this approach will not work always, since Mathematica has an
> odd way to handle approximate numbers. For example,
> 
> In[6]:=
> RealDigits[345.89087]
> Out[6]=
> {{3, 4, 5, 8, 9, 0, 8, 7, 0, 0, 0, 0, 0, 0, 0, 0}, 3}
> 
> but
> 
> In[7]:=
> RealDigits[89087.345]
> Out[7]=
> {{8, 9, 0, 8, 7, 3, 4, 5, 0, 0, 0, 0, 0, 0, 0, 1}, 5}
> 
> and now you get an unexpected (and undesirable) 1 at the end of the sequence
> of digits! It seems that a general approach would have to be of a less
> elegant nature, viz, if you have an integer number, then just use
> ToString[]; otherwise, multiply the number by 10 to the power "number of
> figures to the right of the decimal point", i..e. make it an integer first,
> and then proceed as indicated above, but you must count visually the number
> of significant figures in your number. Example:
> 
> In[8]:=
> c = FixedPoint[zeroAtTheEnd, RealDigits[89087.345*10^3][[1]]]
> Out[8]=
> {8, 9, 0, 8, 7, 3, 4, 5}
> 
> In[9]:=
> ToString[FromDigits[Take[c, 5]]] <> "." <> ToString[FromDigits[Take[c, -3]]]
> Out[9]=
> "89087.345"
> 
> There is probably a much simpler way to do what you want, but this is what
> came to my mind first.
> 
> Tomas Garza
> Mexico City
> 
> 
> 
> 
> 
> 
> 
> 
> ----- Original Message -----
> From: "liwen liwen" <gzgear at yahoo.com>
To: mathgroup at smc.vnet.net
> Subject: [mg26585] [mg26515] How can I transform the number of 123.456 into "123.456"?
> 
> 
> > Dear friend:
> >             Happy New Year!
> > I want to transform the numbers such as 123.456 or
> > 345.89087 into strings as "123.456" or "345.89087" ,
> > Could you help me?
> > Thank you very much!
> >
> > Best regards,
> >
> > Liwen
> > E-mail:  gzgear at yahoo.com
> >
> >  12/30/2000
> >
> >
> >
> > __________________________________________________
> > Do You Yahoo!?
> > Yahoo! Photos - Share your holiday photos online!
> > http://photos.yahoo.com/
> >
> 
> 


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