Re: oddity in putting a conditional in the using clause

[sfeam <sf...@us...>]

On Sunday, 15 March 2015 02:54:48 PM pl...@pi... wrote:
> Hi,
> 
> I seem to have an oddity in putting a conditional in the using clause in 
> v5.0
> 
> 
>   tail longest.dat
> 
> 171  3342.447
> 172  3371.391
> 173  3400.336
> 174  3465.342
> 175  3458.227
> 176  3324.896
> 177  3389.902
> 178  3400.818
> 179  3429.764
> 180  3476.738
> 
> 
> G N U P L O T
>          Version 5.0 patchlevel alpha    last modified 2014-05-10
> 
> 
> 
> 
> gnuplot>  plot  "longest.dat" using (($1/2*2==$1)?NaN:$1):2
> 
>           x range is invalid
> 
> 
> I'm trying to plot for the even  values in col 1.
> if I do :  using (($1/2*2==$1)?$1:NaN):2   it plots every point
> and  using (($1/2*2==$1)?NaN:$1):2 complains that it has an empty x 
> range ( ie using is always returning NaN.

That is because $1/2*2 always equals $1.
You are probably thinking that your column 1 values are integers 
and therefore $1/2 will be truncated to an integer also, but 
that is not the case.  Data values are always read in as (double).

Try 

   plot  "longest.dat" using ((int($1)/2*2==$1)?NaN:$1):2

or maybe

   plot "longest.dat" using ((int($1)&01 == 01) ? $1 : NaN):2



> 
> The syntax of my using clause seem right if I test it in a print:
> 
> gnuplot>   i=179;print (i/2*2==i)?i:NaN
> NaN
> gnuplot>   i=178;print (i/2*2==i)?i:NaN
> 178
> 
> I know I could do this using "every" with that sample data but this is 
> about the syntax not giving expected result.
> 
> Peter.