# PGFPLOTS Marginal Histogram with date data

I took Jake's code from Scatterplot with Marginal Histograms and ran into a problem with trying to histogram date data on the x axis. The scatterplot and y axis histogram work well, revealing:

The code for the top histogram is:

%% The histogram for the x axis
\begin{axis}[
date coordinates in=x, xticklabel={\year}, date ZERO=1996-01-01,
anchor=south west, axis y line*=right, axis x line*=bottom,
at=(main axis.north west), xmin=1996-01-01, xmax=2015-12-01,
height=3cm, yshift=1.2cm, ymajorgrids,
x axis line style={opacity=0}, ymin=0, ymax=25,
xtick=\empty, ytick={0,5,10,15,20,25},
]
%    hist={data=x}, % By default, the y values
%    fill=yellow!50 %would be used for calculating the histogram
%         ] table {bikeplotoa.dat};
\end{axis}


I read that date coordinates in=x, convert the date format to Julean data in Integer form (pg.332). How do I histogram date format data? Is there any way to get this to work with the hist routine?

This is what pdflatex spits out:

! Package PGF Math Error: Could not parse input '1996-01-01' as a
floating point number, sorry.
The unreadable part was near '-01-01'..


The essentail MWE is:

\documentclass[12ptl]{article}
%\usepackage[letterpaper,margin=2cm]{geometry}
\usepackage{pgfplots}
\usepgfplotslibrary{dateplot}

\begin{document}
\begin{center}

\begin{tikzpicture}[
/pgfplots/scale only axis,
/pgfplots/width=0.7\linewidth, %6cm,
/pgfplots/height=0.7\linewidth %6cm
]

% The scatterplot
\begin{axis}[
date coordinates in=x, xticklabel={\year}, date ZERO=1997-10-02,
xtick={1997-01-01,1999-01-01,2001-01-01,2003-01-01,2005-01-01,2007-01-01,2009-01-01,
2011-01-01,2013-01-01,2015-01-01},
minor xtick={1998-01-01,2000-01-01,2002-01-01,2004-01-01,2006-01-01,2008-01-01,
2010-01-01, 2012-01-01,2014-01-01,2016-01-01},
name=main axis, % Name the axis, so we can position
% the histograms relative to this axis
axis y line*=right, axis x line*=top, tick align=outside,
fill=green!50, xmin=1996-01-01, xmax=2015-12-01, ymin=0, ymax=55,
separate axis lines, xmajorgrids, xminorgrids, ymajorgrids,
xlabel=Year, ylabel=Miles, minor tick num=2,
]
\addplot [only marks, mark size=1.5] table {bikeplotoa.dat};
\end{axis}

%% The histogram for the x axis
\begin{axis}[
date coordinates in=x, xticklabel={\year}, date ZERO=1996-01-01,
anchor=south west, axis y line*=right, axis x line*=bottom,
at=(main axis.north west), xmin=1996-01-01, xmax=2015-12-01,
height=3cm, yshift=1.2cm, ymajorgrids,
x axis line style={opacity=0}, ymin=0, ymax=25,
xtick=\empty, ytick={0,5,10,15,20,25},
]
%    hist={data=x}, % By default, the y values
%    fill=yellow!50 %would be used for calculating the histogram
%         ] table {bikeplotoa.dat};

\end{axis}

% The histogram for the y axis
\begin{axis}[ ymin=0, ymax=55,
anchor=north west, axis y line*=left, axis x line*=top,
y axis line style={opacity=0},
at=(main axis.north east), xmajorgrids,
width=4cm, xshift=1.5cm, xmin=0, xmax=160,
ytick=\empty, xtick={0,40,80,120,160},
]
% For swapping the x and y axis, we have to change a couple of options...
hist={handler/.style={xbar interval}, bins=11,
data min=0, data max=55}, % ... use bars instead of columns ...
x filter/.code=\pgfmathparse{rawy}, % ... interpret the x values of the histogram as y values
y filter/.code=\pgfmathparse{rawx}, % ... and vice versa.
fill=blue!50,
] table {bikeplotoa.dat};
\end{axis}
\end{tikzpicture}
\end{center}

\end{document}


The file: bikeplotoa.dat contains 670 lines in the form:

    date       miles
1997-10-02 15.6
1997-10-03 8.6
1997-10-04 12.1
1997-10-05 15.1
1997-10-06 10.5
1997-10-07 2.9
1997-10-08 10.9
1997-10-09 8.1
1997-10-11 13.3
1997-10-12 9.5
1997-10-12 9.5
1997-10-17 7.9
1997-10-18 9
1997-10-23 11.3
1997-10-27 5.7


Regards, Dave

• Couldn't you just use a simple program to convert the dates to floats in the original bikeplotoa.dat file? You could convert the month and day data into fractions of the year and simply plot the resulting floats. Wouldn't this be an easy workaround? – Ben Mar 30 '16 at 14:37

As already seen in Ben's answer it seems that you have to convert the dates to some numeric value to make it work.

I present a solution where I extend your data table by converting the dates with the \pgfcalendardatetojulian command from the pgfcalendar library/package and then use this new column for the histogram.

For more details have a look at the comments in the code.

    % to have at least two bars in the histogram, I have copied the
% data again and changed the year to 2005
\begin{filecontents*}{bikeplotoa.dat}
date       miles
1997-10-02 15.6
1997-10-03 8.6
1997-10-04 12.1
1997-10-05 15.1
1997-10-06 10.5
1997-10-07 2.9
1997-10-08 10.9
1997-10-09 8.1
1997-10-11 13.3
1997-10-12 9.5
1997-10-12 9.5
1997-10-17 7.9
1997-10-18 9
1997-10-23 11.3
1997-10-27 5.7
2005-10-02 15.6
2005-10-03 8.6
2005-10-04 12.1
2005-10-05 15.1
2005-10-06 10.5
2005-10-07 2.9
2005-10-08 10.9
2005-10-09 8.1
2005-10-11 13.3
2005-10-12 9.5
2005-10-12 9.5
2005-10-17 7.9
2005-10-18 9
2005-10-23 11.3
2005-10-27 5.7
\end{filecontents*}
\documentclass[border=2mm]{standalone}
\usepackage{filecontents}
\usepackage{tikz}
\usepackage{pgfcalendar}    % <-- to convert the dates to Julian integers
\usepackage{pgfplots}
\usepackage{pgfplotstable}  % <-- to manipulate the data file/table
\usetikzlibrary{
pgfplots.dateplot,
}
\pgfplotsset{compat=1.3}
% add new column with Julian integer numbers
% therefore a counter is needed
\newcount\julianday
\pgfplotstablecreatecol[
create col/assign/.code={
% convert the number of the current row and save it to \julianday'
\pgfcalendardatetojulian{\thisrow{date}}{\julianday}
% then give the entry of \julianday' to \entry' which is then
% given to the current cell
\edef\entry{\the\julianday}
\pgfkeyslet{/pgfplots/table/create col/next content}\entry
}
]{JulianDay}{\data}

% store xmin' and xmax' values in commands so they can be added as these
% to the corresponding axis values. For that also the "JulianDay" numbers
% are needed
\def\xmin{1996-01-01}
\def\xmax{2015-12-01}
\newcount\xminjulian
\pgfcalendardatetojulian{\xmin}{\xminjulian}
\def\xminJulian{\the\xminjulian}
\newcount\xmaxjulian
\pgfcalendardatetojulian{\xmax}{\xmaxjulian}
\def\xmaxJulian{\the\xmaxjulian}
\begin{document}

%% show resulting numbers, if you want
%\pgfplotstabletypeset[
%    column type=l,
%    columns={date,JulianDay},
%    columns/date/.style={string type},
%    columns/JulianDay/.style={numeric as string type},
%]\data
%
%% here you can see the resulting numbers for xmin' and xmax'
%\xminJulian, \xmaxJulian

\begin{tikzpicture}[
/pgfplots/scale only axis,
/pgfplots/width=0.7\linewidth, %6cm,
/pgfplots/height=0.7\linewidth %6cm
]

% The scatterplot
\begin{axis}[
date coordinates in=x,
xticklabel=\year,
date ZERO=1997-10-02,
%        xtick={1997-01-01,1999-01-01,2001-01-01,2003-01-01,2005-01-01,2007-01-01,2009-01-01,
%               2011-01-01,2013-01-01,2015-01-01},
%        minor xtick={1998-01-01,2000-01-01,2002-01-01,2004-01-01,2006-01-01,2008-01-01,
%                     2010-01-01, 2012-01-01,2014-01-01,2016-01-01},
name=main axis, % Name the axis, so we can position
% the histograms relative to this axis
axis y line*=right,
axis x line*=top,
tick align=outside,
fill=green!50,
xmin=\xmin,
xmax=\xmax,
ymin=0,
ymax=55,
separate axis lines,
xmajorgrids,
xminorgrids,
ymajorgrids,
xlabel=Year,
ylabel=Miles,
minor tick num=2,
]
\addplot [only marks, mark size=1.5] table {\data};
\end{axis}

%% The histogram for the x axis
\begin{axis}[
anchor=south west,
axis y line*=right,
axis x line*=bottom,
at=(main axis.north west),
% use calculated values so they match the values of the scatterplot
xmin=\xminJulian,
xmax=\xmaxJulian,
height=3cm,
yshift=1.2cm,
ymajorgrids,
x axis line style={opacity=0},
ymin=0,
ymax=25,
xtick=\empty,
ytick={0,5,10,15,20,25},
]
hist={data=x},
fill=yellow!50,
] table [x=JulianDay,y=miles] {\data};
\end{axis}

% The histogram for the y axis
\begin{axis}[
ymin=0,
ymax=55,
anchor=north west,
axis y line*=left,
axis x line*=top,
y axis line style={opacity=0},
at=(main axis.north east),
xmajorgrids,
width=4cm,
xshift=1.5cm,
xmin=0,
xmax=160,
ytick=\empty,
xtick={0,40,80,120,160},
]
% For swapping the x and y axis, we have to change a couple of options...
hist={
handler/.style={
xbar interval,
},
bins=11,
data min=0,
data max=55, % ... use bars instead of columns ...
},
x filter/.code=\pgfmathparse{rawy}, % ... interpret the x values of the histogram as y values
y filter/.code=\pgfmathparse{rawx}, % ... and vice versa.
fill=blue!50,
] table {\data};
\end{axis}
\end{tikzpicture}
\end{document}


• I awarded the bounty to you for the solotion being Latex only. Great work. – JMP Apr 3 '16 at 21:13

I wrote a little Python program to convert the yyyy-mm-dd dates into floating point numbers, which should approximately match the according positions on the time axis.

import re

f = open('floatdates.dat','w')

pattern = r'(\d+)-(\d+)-(\d+)\t([\d.]+)'
for line in open('data.dat'):
data = re.findall(pattern,line)

if len(data)>0:
floatdate = int(data[0][0]) + (float(data[0][1])-1)/12 + (float(data[0][2])-1)/365
f.write('%f\t%s\n' % (floatdate,data[0][3]))

f.close()


It converts your given sample file to the following.

1997.752740     15.6
1997.755479     8.6
1997.758219     12.1
1997.760959     15.1
1997.763699     10.5
1997.766438     2.9
1997.769178     10.9
1997.771918     8.1
1997.777397     13.3
1997.780137     9.5
1997.780137     9.5
1997.793836     7.9
1997.796575     9
1997.810274     11.3


This can then be used in the scatterplot with marginal histograms you mentioned. Using that I obtained the following result. It doesn't look fantastic, but you can tweak the layout, if you want.

For completeness I include the .tex Code:

\documentclass{article}

\usepackage{pgfplots}

\begin{document}

\begin{tikzpicture}[
/pgfplots/scale only axis,
/pgfplots/width=6cm,
/pgfplots/height=6cm
]

% The scatterplot
\begin{axis}[
name=main axis, % Name the axis, so we can position the histograms relative to this axis
x tick label style={
/pgf/number format/.cd,
fixed,
fixed zerofill,
precision=0,
/tikz/.cd
}
]
\addplot [only marks, mark size=1.5] table {floatdates.dat};
\end{axis}

% The histogram for the x axis
\begin{axis}[
anchor=south west,
at=(main axis.north west),
height=2cm,
xtick=\empty
]
hist={data=x}, % By default, the y values would be used for calculating the histogram
fill=gray!50
] table {floatdates.dat};
\end{axis}

% The histogram for the y axis
\begin{axis}[
anchor=north west,
at=(main axis.north east),
width=2cm,
ytick=\empty
]
`