Re: what is the use of "u" in tabulated output?

[<pl...@pi...>]

On 04/23/14 21:05, Ethan A Merritt wrote:
>
> On Wednesday, 23 April, 2014 20:50:18 pl...@pi... wrote:
>> On 04/23/14 20:30, Ethan A Merritt wrote:
>>>
>>> On Sunday, 20 April, 2014 11:02:48 pl...@pi... wrote:
>>>> On 04/20/14 10:48, pl...@pi... wrote:
>>>>>
>>>>> I often use conditional using clauses to plot part of a range of data
>>>>>
>>>>> plot datafile using   (($1<=1995.55)?$1:NaN):(2*fcos1($1))
>>>
>>> [defer discussion of tabular output to a separate reply]
>>>
>>>> I've just found out the if I used "NaN" as a string instead of NaN in
>>>> the using clause I get the result I expected: the data cuts off at the
>>>> required date.
>>>>
>>>> plot datafile using   (($1<=1995.55)?$1:"NaN"):(2*fcos1($1))
>>>
>>> I think that's because you gave a string where a number was expected.
>>> The fact that the string contained "NaN" rather than, say, "foo" is not
>>> relevant.
>>>
>>>> It seems there is an inconsistency in the way this is being handled.
>>>
>>> I agree. This is a bug.  If the program finds a string where a number
>>> was expected, the numerical value returned to get_data() should be
>>> NaN rather than some random or left-over value from an earlier line.
>>> This should get a fix for both 4.6 and 5.
>>>
>>> 	Ethan
>>>
>>
>> I would have expected the parser the throw this out since it is
>> illegitimate input in this context.
>>
>> I only tried this to see what would happen when the correct syntax
>> produced garbage output.
>>
>> Why didn't the parser reject it ?
>
> It's fine at the level of parsing.  There's nothing intrinsically wrong
> with reading in a data string rather than a number.  The problem
> only comes later if you try to use that for something that really does
> require a numerical value.   The bug is that there is still an old
> numerical value hanging around from an earlier read operation that
> is used instead.  That shouldn't happen.
>
> 	Ethan
>
>
>


OK, I was forgetting that a string can be valid as a 'using' specifier 
for named columns. You are correct ( as often happens ;) ).


However, here's another oddity:

gnuplot> plot "-" u ("foo"):2
input data ('e' ends) > 1 2
input data ('e' ends) > e
Warning: empty x range [1.58805e-314:1.58805e-314], adjusting to 
[1.57217e-314:1.60393e-314]
Warning: empty y range [2:2], adjusting to [1.98:2.02]


Why is the string "foo" being evaluated as something close to zero? If I 
try addition it does not get interpreted as zero, it gets kicked out:

  x=1+"foo"
          Non-numeric string found where a numeric expression was expected


Here's another bug:

gnuplot> plot "-" u ("foo"):2
input data ('e' ends) > 1 2
input data ('e' ends) > 3 4
input data ('e' ends) > e

This produces two '+'  marks at the extreme left of the wxt window: 
outside the plot area !

There is no x-axis labelling nor grid, though I do get y axis and grid 
lines.


Unless you see any mistakes here, maybe these should be split to 
separate messages too.


/Peter.