[R] Format wanted...

[Duncan Murdoch]

On 12-03-25 10:45 AM, Marc Schwartz wrote:
>
> On Mar 25, 2012, at 7:14 AM, Duncan Murdoch wrote:
>
>> On 12-03-24 10:47 PM, J Toll wrote:
>>> On Sat, Mar 24, 2012 at 7:30 PM, Duncan Murdoch
>>> <murdoch.duncan at gmail.com>   wrote:
>>>> Do we have a format that always includes a decimal point and a given number
>>>> of significant digits, but otherwise drops unnecessary characters?  For
>>>> example, if I wanted 5 digits, I'd want the following:
>>>>
>>>> Round to 5 digits:
>>>> 1.234567  ->   "1.2346"
>>>>
>>>> Drop unnecessary zeros:
>>>> 1.23      ->   "1.23"
>>>>
>>>> Force inclusion of a decimal point:
>>>> 1         ->   "1."
>>>>
>>>
>>> Duncan,
>>>
>>> Maybe sprintf() will work for you.  As it's a wrapper for C sprintf,
>>> it should have its functionality.
>>
>> Maybe, but with which format string?
>>
>> Duncan Murdoch
>
>
> I don't believe (though could be wrong), that you can do it all with one format string, but can do it conditionally based upon the input. According to the C printf documentation, the use of "#" forces a decimal point to be present, even if there are no trailing digits. Thus:
>
>> sprintf("%#.f", 1)
> [1] "1."
>
> The other two values seem to be handled by signif() when applied to each value individually:
>
>> signif(1.234567, 5)
> [1] 1.2346
>
>> signif(1.23, 5)
> [1] 1.23
>
> But, not when a vector:
>
>> signif(c(1.234567, 1.23), 5)
> [1] 1.2346 1.2300
>
>
> So, wrapping that inside a function, using ifelse() to test for an integer value:
>
> signif.d<- function(x, digits)
> {
>    ifelse(x == round(x),
>           sprintf("%.#f", x),
>           signif(x, digits))
> }
>
>
> x<- c(1.234567, 1.23, 1)
>
>> signif.d(x, 5)
> [1] "1.2346" "1.23"   "1."
>
>> signif.d(x, 6)
> [1] "1.23457" "1.23"    "1."
>
>> signif.d(x, 7)
> [1] "1.234567" "1.23"     "1."
>
>
> Not extensively tested of course, but hopefully that might work for your needs Duncan.

Thanks.  I had put together a different conditional (just do the 
conversion, then add a decimal point at the end if none is seen), but I 
was surprised that there was no standard format for this.

In case anyone is interested, I want to output code in a language (GLSL) 
that sees 1 and 1. as different types.  I want a floating point value, 
so I need the decimal point.

Duncan Murdoch