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Re: st: variable format (graphics example)


From   Nick Cox <[email protected]>
To   [email protected]
Subject   Re: st: variable format (graphics example)
Date   Fri, 11 Mar 2011 08:52:04 +0000

"beyond the first" should be "beyond the second"

On Fri, Mar 11, 2011 at 8:39 AM, Nick Cox <[email protected]> wrote:
> Much depends on precisely what you mean by "works" but -string()-
> followed by -destring- can't get around the limits to precision
> either. It's just a roundabout way of going, in your case,
>
> gen double rvar = round(var, 0.01)
>
> Set your variable's display format to say %23.18f and you will see
> that there are higher decimal digits beyond the first in all (or
> almost all) values. (Numbers ending in .5 can be held exactly, for
> example.)
>
> Nick
>
> On Fri, Mar 11, 2011 at 6:09 AM, Andreas Drichoutis <[email protected]> wrote:
>
>> It worked. I first used                 generate rvar = string( var ,
>> "%9.2f")
>> and then                        destring rvar, replace
>>
>> this also works:                tostring  var, g(rvar) format(%9.2f) force
>>
>> my new variable has exactly 2 decimal points.
>>
> Nick Cox
>
>> Several misconceptions, some old, some new, have surfaced in this thread.
>>
>> -round()-'s main role is to round to the nearest integer: that's the
>> one argument version.
>>
>> It allows a second argument, but nothing in that overturns the limits
>> to decimal precision implied by binary numbers. While the effect of
>>
>> . di round(42.42, 1)
>> 42
>>
>> is clear, using -round()- to multiples of 0.01 implies just "convert
>> this number as closely as you can to a multiple of 0.01". So, even if
>> at first sight it seems that in this example
>>
>> . di round(42.42, 0.1)
>> 42.4
>>
>> the rounding succeeded, that is just an illusion caused by the lens of
>> the display format implied here. In fact the result is not exactly
>> 42.4 at all:
>>
>> . di %23.18f round(42.42, 0.1)
>>  42.400000000000006000
>>
>> Either way, as has been pointed out, using a display format for the
>> purpose is the way to get numbers displayed as you wish.
>>
>> Finally, -tostring- is a convenience and safety-conscious command for
>> converting a bundle of variables at once. But whenever you know that
>> you want a string variable and that you want to trim away
>> representations of high decimal places, then doing it directly with
>>
>> generate ru = string(u , "%9.2f")
>>
>> is the way to do it. There is nothing wrong with using -tostring- for
>> the purpose, but it is firing up a command with two hundred lines of
>> Stata code for iteration, caution and special cases when a one-line
>> command gets you there directly. In fact, the -string()- function long
>> predates -tostring- and -tostring- is just an elaborate wrapper for
>> -string()-, so it's bizarre to see that being overlooked.
>>
>> Of course, -tostring- is a great command when you really need it.
>>
>> Nick
>>
>> On Thu, Mar 10, 2011 at 10:12 PM, Feiveson, Alan H. (JSC-SK311)
>> <[email protected]> wrote:
>>
>>> Daniel - That's because I was trying to implement -tostring- by hand!
>>>
>>> Thanks for making me aware of it.
>>
>> Daniel Klein
>>
>>> Changing
>>>
>>> . gen ru = round(u,.01)
>>>
>>> to
>>>
>>> . tostring u ,g(ru) format(%9.2f) force
>>>
>>> in your example, might be what you are looking for. However, I do not see
>> how this is "too much work", so probably I don't see the point.
>

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