#96 dateplot - values shifted by 1 day

[Torbjorn]

I don't know what causes this, but I can't really see anything wrong with the code, so it looks like a bug. It comes from tex.stackexchange.com/questions/277311/

The code and output is as follows:

\documentclass{standalone}
\usepackage{pgfplots}
\usepgfplotslibrary{dateplot}
\usepackage{filecontents}
\begin{filecontents*}{data.csv}
date,value
2015-01-01, 3.2
2015-01-04, 6.5
2015-01-10, 6.8
\end{filecontents*}
\begin{document}
\begin{tikzpicture}
\centering
\begin{axis}[
    date coordinates in=x,
    xticklabel={\day-\month},
% either of the following two options fixes the problem
%    xtick=data
%    date ZERO=2015-01-01
]
\addplot table [x=date, y=value, col sep=comma] {data.csv};
\end{axis}
\end{tikzpicture}
\end{document}

As you can see the points are one day to the left of the corresponding ticks, e.g. the last point for January 10 is placed on January 9.

[Torbjorn]

Oops, sorry about the size of the image, and lack of hyperlink. Doesn't appear to be possible to edit either.

[Christian Feuersänger]

Thanks for the report.

I see the problem, and I can explain it.

I'll have to think about ways to solve it.

The problem becomes apparent with additional debug logging. Apparently, the automatic tick computation results in the following numeric representations of the tick labels:

3287.9985000000000->2015-01-01, 23:58
3289.9985000000000->2015-01-03, 23:58
3291.9985000000000->2015-01-05, 23:58
3293.9985000000000->2015-01-07, 23:58
3295.9985000000000->2015-01-09, 23:58

xtick=data results in

3287.000000000->2015-01-01, 0:0
3290.00000000->2015-01-04, 0:0
3296.000000000->2015-01-10, 0:0

Thus, it is an accuracy issue combined with the special string to number mapping of the dateplot lib.

Note that if you use a non-date plot with the x coordinates 3287, 3290, and 3296, the tick labels are fine -- since they are rounded. If the dateplot lib would also round to full days, all would be fine as well... perhaps I need to round to 2 digits before I map back to date strings?

[Christian Feuersänger]

Another possible solution may be to ensure that 'date ZERO' is set to a useful value, even if the user did not provide one.

[Christian Feuersänger]

I have ensured that 'date ZERO' is set to the first encountered date if it is not set manually.

This appears to solve the issue.

The fix will be part of pgfplots 1.13