# Heatmaps, matrix plots, imagesc and data structure

If one has a matrix, say:

16     2     3    13
5    11    10     8
9     7     6    12
4    14    15     1


This is possibly stored in a .dat file as shown above, and possible to have thousands of entries in each direction One might like the idea of plotting it as a heatmap/surface. This is possible in many ways:

# The matrix plot:

Restructure the file to:

x   y   C
0   0   16
0   1    5
0   2    9
0   3    4

1   0    2
1   1   11
1   2    7
1   3   14

2   0    3
2   1   10
2   2    6
2   3   15

3   0   13
3   1    8
3   2   12
3   3    1


and do something like:

\documentclass[border=5pt]{standalone}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{pgfplots}
\pgfplotsset{compat=1.15}
\begin{document}
\begin{tikzpicture}
\begin{axis}[colorbar]
nodes near coords=\coordindex,
mark=*,
mesh/cols=4,
\end{axis}
\end{tikzpicture}
\end{document}


To get:

(Ideally without the numbers, but with the axis (So the ticks can be controlled)) Advantages:

• works with all the colormaps build into pgfplots
• Easily formatable as any other axis environment

• Needs data to be restructured, which is annoying for our larger matrices (this is a super big downside, for using the same data in "fast"--show the supervisor plots and "slow"--use in thesis plots)

# The table heatmap:

There are multiple ways to convert tables to heatmaps:

Parametrize shading in table through TikZ

https://texblog.org/2013/06/13/latex-heatmap-using-tabular/

• The data is in nice files

• The colormaps aren't always all availiable, since the solutions aren't directly incorperated in pgfplots/tikz
• They are tables, and thus aren't as configurable as

# What I really want

Is something comparable to the function imagesc availiable in MATLAB and R. My biggest gripe is having to restructure the data (even with a script) as it's nice to be able to chechk the data fast in MATLAB and then decide how to design the LaTeX plot from there.

pgfplots: Reshape a MATRIX of data before conditional 3D surface plotting

Plot and imagesc (from Matlab) with PSTricks

matlab2tikz imagesc TikZ/pgfplots equivalent

None of the above are great at reading the ´´matrix shaped´´ data, directly from LaTeX.

• I'm not sure what your desired input and output look like. Is the post tex.stackexchange.com/questions/401370/… related? – Andrew Sep 27 '18 at 14:13
• I would like not to have values shown, and have an x and y axis on there – Thorbjørn E. K. Christensen Sep 27 '18 at 14:14
• Please don't edit your question so that it invalidates existing answers. They went to a lot of trouble to write those answers. If you want to contribute your answer as well, that will be fine. If you still have a question remaining, you should consider asking a new question. – Teepeemm Oct 3 '18 at 11:42
• @Teepeemm I wasn't trying to invalidate them, Sorry about that, I've moved the edit to an answer. – Thorbjørn E. K. Christensen Oct 3 '18 at 11:52

Some time back I wrote some macros that convert the data format you start with to the one you got after "restructuring" the data automatically. At the time I wrote these, I thought there must be a much simpler way. However, I did not see a simpler way so far, and nobody complained. So perhaps this is the way to go:

2. Convert the data to the matrix format and store it in a table.
3. Use this new table in a matrix plot.

Here are code and result.

\documentclass[border=3.14mm,tikz]{standalone}
\usepackage{pgfplots}
\usetikzlibrary{pgfplots.colormaps}
\pgfplotsset{compat=1.16}
\usepackage{pgfplotstable}
\usepackage{filecontents}

\begin{filecontents*}{entries.dat}
16     2     3    13
5    11    10     8
9     7     6    12
4    14    15     1
\end{filecontents*}
\pgfplotstablegetelem{#2}{[index]#3}\of{#1}%
\let#4\pgfplotsretval
}
\begin{document}
\pgfplotstablegetrowsof{\datatable}
\pgfmathtruncatemacro{\numrows}{\pgfplotsretval}
\pgfplotstablegetcolsof{\datatable}
\pgfmathtruncatemacro{\numcols}{\pgfplotsretval}
\xdef\LstX{}
\xdef\LstY{}
\xdef\LstC{}
\foreach \Y [evaluate=\Y as \PrevY using {int(\Y-1)},count=\nY] in {1,...,\numrows}
{\pgfmathtruncatemacro{\newY}{\numrows-\Y}
\foreach \X  [evaluate=\X as \PrevX using {int(\X-1)},count=\nX] in {1,...,\numcols}
{
\pgfmathtruncatemacro{\nZ}{\nX+\nY}
\ifnum\nZ=2
\xdef\LstX{\PrevX}
\xdef\LstY{\PrevY}
\xdef\LstC{\Current}
\else
\xdef\LstX{\LstX,\PrevX}
\xdef\LstY{\LstY,\PrevY}
\xdef\LstC{\LstC,\Current}
\fi
}
}
\edef\temp{\noexpand\pgfplotstableset{
create on use/x/.style={create col/set list={\LstX}},
create on use/y/.style={create col/set list={\LstY}},
create on use/color/.style={create col/set list={\LstC}},}}
\temp
\pgfmathtruncatemacro{\strangenum}{\numrows*\numcols}
\pgfplotstablenew[columns={x,y,color}]{\strangenum}\strangetable

%\pgfplotstabletypeset[empty cells with={---}]\strangetable
\begin{tikzpicture}
% \pgfplotsset{%
%     colormap={WhiteRedBlack}{%
%         rgb255=(255,255,255)
%         rgb255=(255,0,0)
%         rgb255=(0,0,0)
%     },
% }
\begin{axis}[%
small,
every tick label/.append style={font=\tiny},
tick align=outside,
minor tick num=5,
%
xlabel=$\beta$,
xticklabel pos=right,
xlabel near ticks,
xmin=-1, xmax=5,
xtick={0, 5, ..., 4},
%
ylabel=$\alpha$,
ylabel style={rotate=-90},
ymin=-1, ymax=5,
ytick={0, 5, ..., 4},
%
%     point meta min=0,
%     point meta max=32,
point meta=explicit,
%
%colorbar sampled,
colorbar as palette,
colorbar style={samples=3},
%colormap name=WhiteRedBlack,
scale mode=scale uniformly,
]
\draw (axis description cs:0,0) -- (axis description cs:1,0);
matrix plot,
%mesh/cols=4,
point meta=explicit,
] table [meta=color,col sep=comma] \strangetable;
\end{axis}
\end{tikzpicture}
\end{document}


BTW, the numbers you want to get rid of are nodes near coords. If you don't want them, just don't add them. And in my previous answer I also had a pgfplots-less method which is very similar, at least in spirit, to Steven's nice answer. Of course, using these methods, on the long run one may suffer from the fact that one cannot access some of the really cool features of pgfplots like 3d or color maps.

• Super nice answer ;-) For some reason I got a huge whitespace to the left of the figure, but moving everything between \begin{document} and \begin{tikzpicture} into the preamble fixed that. – Thorbjørn E. K. Christensen Oct 1 '18 at 14:11
• @ThorbjørnE.K.Christensen Strange, on my machine there is no whitespace generated but I am glad you could fix it. Saying \documentclass[border=3.14mm,tikz]{standalone} should in principle take care of any possible white space, and it does no my machine. Anyway, glad to hear you like the answer. ;-) – user121799 Oct 1 '18 at 14:18
• after commenting I saw that I had written \documentclass[border=5pt,tiz]{standalone} (corrected now) but I would still expect there to be no whitespace. – Thorbjørn E. K. Christensen Oct 1 '18 at 14:49
• @ThorbjørnE.K.Christensen The standalone class can be tricky with regards to whitespace but it also allows you to define environments that should be cropped, such as tikz in this example. I would think (but did not test) that if you include the code in an article, there won't be whitespace. – user121799 Oct 1 '18 at 14:52
• There wasn't any (I tried to see what \strangetable looked like) But when in standalone there was tons of whitespace (which I thought was curious). I've moved the command to a macro, so I can use it at multiple places. – Thorbjørn E. K. Christensen Oct 1 '18 at 14:55

Don't know if this is helpful, but I wanted to try it.

\plotit[<scale reference>]{<filename>}


where <scale reference> is the value, greater than any table entry, that serves as the 100% saturation value.

I also have a version where you can enter data directly:

\begin{stackColor}[<scale reference>]
23  4   77 \\
15  99  33\\
87  0   5 \\
97  33  55
\end{stackColor}


The default scale reference is 100. There are two parameters to change appearance: \cellwd defines the width/height of the color block, plotcolmax defines the fully saturated color of the plot, and plotcolmin defines the fully unsaturated color of the plot. You need to use \colorlet as in \colorlet{plotcolmax}{cyan!50}.

I have set it up so that the plot sits on the baseline.

EDITED to provide legend capability with \makelegend[<rule thickness>]{<units>}. The optional argument is the thickness of the surrounding \fbox and scale lines (default \fboxrule). Units have been added as a mandatory argument. The legend uses two settable parameters.

\def\legendwd{6pt}
\def\legendht{30pt}


to define the legend colorbar dimension. It will print the legend where invoked, again sitting on the baseline.

REEDIT: While I don't know tikz, I groped around enough to cobble together how to insert the lot on a set of axes.

EDITED to add the cool pdq.dat data (based on sample data found at http://psy.swansea.ac.uk/staff/carter/gnuplot/gnuplot_3d.htm)

The MWE:

\documentclass{article}
tabstackengine,etoolbox,pgfplots}
\usetikzlibrary{snakes}
\begin{filecontents*}{mydata.dat}
16     2     3    13
5    11    10     8
9     7     6    12
4    14    15     1
\end{filecontents*}
\begin{filecontents*}{pdq.dat}
000 010 019 028 036 042 047 049 050 049 045 040 034 026 017 007
010 020 029 038 046 052 057 059 060 059 055 050 044 036 027 017
019 029 039 048 055 062 066 069 069 068 065 060 053 045 036 027
028 038 048 056 064 070 075 078 078 077 074 069 062 054 045 035
036 046 055 064 072 078 082 085 086 085 081 076 070 062 053 043
042 052 062 070 078 084 089 091 092 091 088 082 076 068 059 049
047 057 066 075 082 089 093 096 097 095 092 087 080 072 063 054
049 059 069 078 085 091 096 099 099 098 095 090 083 075 066 056
050 060 069 078 086 092 097 099 100 099 095 090 084 076 067 057
049 059 068 077 085 091 095 098 099 097 094 089 082 074 065 056
045 055 065 074 081 088 092 095 095 094 091 086 079 071 062 053
040 050 060 069 076 082 087 090 090 089 086 081 074 066 057 047
034 044 053 062 070 076 080 083 084 082 079 074 068 060 051 041
026 036 045 054 062 068 072 075 076 074 071 066 060 052 043 033
017 027 036 045 053 059 063 066 067 065 062 057 051 043 033 024
007 017 027 035 043 049 054 056 057 056 053 047 041 033 024 014
\end{filecontents*}
%%%%%%%%%%%%%
\def\cellwd{15pt}
\colorlet{plotcolmax}{cyan}
\colorlet{plotcolmin}{yellow!20}
\def\legendwd{6pt}
\def\legendht{30pt}
%%%%%%%%%%%%%
\newlength\dlegend
\newcounter{legcnt}
\newtoks\tabAtoks
\newcount\plotvalue
\newcommand\apptotoks[2]{#1\expandafter{\the#1#2}}
\NewEnviron{stackColor}[1][100]{%
\ignoreemptyitems%
\def\tAtmp{plotcolmax!}%
\tabcolsep=0pt\relax%
\setsepchar{\\/ }%
\tabAtoks{}%
\foreachitem\i\in\tabA[]{%
\ifnum\listlen\tabA[\icnt]>1\relax%
\foreachitem\j\in\tabA[\icnt]{%
\expandafter\plotvalue\j\relax%
\multiply\plotvalue by 100%
\divide\plotvalue by #1%
\xdef\plotmax{#1}%
\ifnum\jcnt=1\relax\else\apptotoks\tabAtoks{&}\fi%
\expandafter\apptotoks\expandafter\tabAtoks\expandafter{%
\expandafter\textcolor\expandafter{\expandafter\tAtmp%
\the\plotvalue!plotcolmin}{\rule{\cellwd}{\cellwd}}}%
}%
\ifnum\icnt<\listlen\tabA[]\relax\apptotoks\tabAtoks{%
\\}\fi%
\fi%
}%
\def\tmp{\setstackgap{S}{0pt}\tabbedShortstack}%
\expandafter\tmp\expandafter{\the\tabAtoks}%
}
\newcommand\plotit[2][100]{%
\def\tmp{\begin{stackColor}[#1]}%
\expandafter\tmp\mydata\end{stackColor}%
}
\newcommand\makelegend[2][\fboxrule]{{%
\dlegend=\legendht%
\divide\dlegend by 101%
\setcounter{legcnt}{0}%
\savestack\thelegend{}%
\setstackgap{S}{0pt}%
\whileboolexpr{test {\ifnumcomp{\thelegcnt}<{101}}}{%
\savestack\thelegend{\stackon{\thelegend}{\textcolor{%
plotcolmax!\thelegcnt!plotcolmin}{\rule{\legendwd}{\dlegend}}}}%
\stepcounter{legcnt}%
}%
\fboxrule#1\relax\fboxsep=0pt\relax\fbox{\thelegend}%
\def\plottick{\rule[.5\dimexpr-\dp\strutbox+\ht\strutbox]{5pt}{%
\fboxrule}}%
\raisebox{.5\dimexpr\dp\strutbox-\ht\strutbox-\fboxrule}{%
\def\stackalignment{l}%
\stackon[\dimexpr\legendht]{\smash{\plottick0}}{\smash{%
\plottick\plotmax\ #2}}%
}%
}}
\begin{document}
Here is my plot:
\begin{stackColor}[99]
23  4   77 \\
15  99  33\\
87  0   5 \\
97  33  55
\end{stackColor}
~\makelegend[.1pt]{\unskip$^\circ$}
{%
\def\cellwd{5pt}
\colorlet{plotcolmax}{blue!90}
\colorlet{plotcolmin}{yellow!80}
\def\legendwd{8pt}
\def\legendht{40pt}
\plotit[100]{pdq.dat}
~\makelegend[.1pt]{Pa}
}

$\def\cellwd{23pt} \colorlet{plotcolmax}{red} y = \left\{\vcenter{\hbox{\plotit[16]{mydata.dat}}}\right\}$

\begin{tikzpicture}
\colorlet{plotcolmax}{blue!50!green}
\def\cellwd{1.5cm}
\def\legendwd{12pt}
\def\legendht{50pt}
% PLOT
\node[anchor=south west,xshift=-3.5pt, yshift=-3.5pt] at (0,0) {%
\plotit[20]{mydata.dat}};
\node(b) at (7,4) {\makelegend{psi}};
% AXES
\draw[->] (0,0) -- coordinate (x axis mid) (6.5,0);
\draw[->] (0,0) -- coordinate (y axis mid) (0,6.5);
% TICKS
\foreach \x in {0,5,...,30}
\draw ({.2*\x},1pt) -- ({.2*\x},-3pt)
node[anchor=north] {\x};
\foreach \y in {0,5,...,30}
\draw (1pt,{.2*\y}) -- (-3pt,{.2*\y})
node[anchor=east] {\y};
%LABELS
\node[below=0.8cm] at (x axis mid) {$x$ (cm)};
\node[rotate=90, above=0.8cm] at (y axis mid) {$y$ (cm)};
\end{tikzpicture}
\end{document}


Ref: Based on my answer at Ensuring consistent formatting for tabular

SUPPLEMENT

Here is a version that can take real data, rather than just integer data, as in the version above. Because I use TeX tricks for converting values into lengths and then stripping points (rather than a more sophisticated tikz approach to multiplication), I haven't explored the extent to which under or overflows might affect the result.

The one limitation is that the <scale reference> is only parsed to the 1/1000 place, so any digits after that are lost.

As you can see in the MWE below, all 4 pics are different as the scale reference is changed, successively, from 1 to 1.2 to 1.29 to 1.299, always operating on the pdq.dat data.

\documentclass{article}
tabstackengine,etoolbox,pgfplots}
\usetikzlibrary{snakes}
\makeatletter\let\strippt\strip@pt\makeatother
\def\mytrunc#1.#2\relax{#1}
\def\mymult#1.#2#3#4#5\relax{%
#1\ifx.#2000\else%
#2\ifx.#300\else%
#3\ifx.#40\else%
#4\fi\fi\fi%
}% MULT BY x1000
\begin{filecontents*}{mydata.dat}
16     2     3    13
5    11    10     8
9     7     6    12
4    14    15     1
\end{filecontents*}
\begin{filecontents*}{pdq.dat}
0.00 0.10 0.19 0.28 0.36 0.42 0.47 0.49 0.50 0.49 0.45 0.40 0.34 0.26 0.17 0.07
0.10 0.20 0.29 0.38 0.46 0.52 0.57 0.59 0.60 0.59 0.55 0.50 0.44 0.36 0.27 0.17
0.19 0.29 0.39 0.48 0.55 0.62 0.66 0.69 0.69 0.68 0.65 0.60 0.53 0.45 0.36 0.27
0.28 0.38 0.48 0.56 0.64 0.70 0.75 0.78 0.78 0.77 0.74 0.69 0.62 0.54 0.45 0.35
0.36 0.46 0.55 0.64 0.72 0.78 0.82 0.85 0.86 0.85 0.81 0.76 0.70 0.62 0.53 0.43
0.42 0.52 0.62 0.70 0.78 0.84 0.89 0.91 0.92 0.91 0.88 0.82 0.76 0.68 0.59 0.49
0.47 0.57 0.66 0.75 0.82 0.89 0.93 0.96 0.97 0.95 0.92 0.87 0.80 0.72 0.63 0.54
0.49 0.59 0.69 0.78 0.85 0.91 0.96 0.99 0.99 0.98 0.95 0.90 0.83 0.75 0.66 0.56
0.50 0.60 0.69 0.78 0.86 0.92 0.97 0.99 1.00 0.99 0.95 0.90 0.84 0.76 0.67 0.57
0.49 0.59 0.68 0.77 0.85 0.91 0.95 0.98 0.99 0.97 0.94 0.89 0.82 0.74 0.65 0.56
0.45 0.55 0.65 0.74 0.81 0.88 0.92 0.95 0.95 0.94 0.91 0.86 0.79 0.71 0.62 0.53
0.40 0.50 0.60 0.69 0.76 0.82 0.87 0.90 0.90 0.89 0.86 0.81 0.74 0.66 0.57 0.47
0.34 0.44 0.53 0.62 0.70 0.76 0.80 0.83 0.84 0.82 0.79 0.74 0.68 0.60 0.51 0.41
0.26 0.36 0.45 0.54 0.62 0.68 0.72 0.75 0.76 0.74 0.71 0.66 0.60 0.52 0.43 0.33
0.17 0.27 0.36 0.45 0.53 0.59 0.63 0.66 0.67 0.65 0.62 0.57 0.51 0.43 0.33 0.24
0.07 0.17 0.27 0.35 0.43 0.49 0.54 0.56 0.57 0.56 0.53 0.47 0.41 0.33 0.24 0.14
\end{filecontents*}
%%%%%%%%%%%%%
\def\cellwd{15pt}
\colorlet{plotcolmax}{cyan}
\colorlet{plotcolmin}{yellow!20}
\def\legendwd{6pt}
\def\legendht{30pt}
%%%%%%%%%%%%%
\newlength\dlegend
\newcounter{legcnt}
\newtoks\tabAtoks
\newcount\plotvalue
\newlength\pvlen
\newcommand\apptotoks[2]{#1\expandafter{\the#1#2}}
\NewEnviron{stackColor}[1][100]{%
\ignoreemptyitems%
\def\tAtmp{plotcolmax!}%
\tabcolsep=0pt\relax%
\setsepchar{\\/ }%
\tabAtoks{}%
\foreachitem\i\in\tabA[]{%
\ifnum\listlen\tabA[\icnt]>1\relax%
\foreachitem\j\in\tabA[\icnt]{%
\expandafter\pvlen\j pt\relax%
\edef\tmp{\mymult#1.000\relax}% IN CASE BARE INTEGER, PAD TO 1/1000 DECIMAL
\divide\pvlen by \tmp%
\multiply\pvlen by 100000% BY 100 x1000
\edef\tmp{\strippt\pvlen}%
\edef\tmp{\expandafter\mytrunc\tmp.\relax}%
\plotvalue=\tmp\relax%
\xdef\plotmax{#1}%
\ifnum\jcnt=1\relax\else\apptotoks\tabAtoks{&}\fi%
\expandafter\apptotoks\expandafter\tabAtoks\expandafter{%
\expandafter\textcolor\expandafter{\expandafter\tAtmp%
\the\plotvalue!plotcolmin}{\rule{\cellwd}{\cellwd}}}%
}%
\ifnum\icnt<\listlen\tabA[]\relax\apptotoks\tabAtoks{%
\\}\fi%
\fi%
}%
\def\tmp{\setstackgap{S}{0pt}\tabbedShortstack}%
\expandafter\tmp\expandafter{\the\tabAtoks}%
}
\newcommand\plotit[2][100]{%
\def\tmp{\begin{stackColor}[#1]}%
\expandafter\tmp\mydata\end{stackColor}%
}
\newcommand\makelegend[2][\fboxrule]{{%
\dlegend=\legendht%
\divide\dlegend by 101%
\setcounter{legcnt}{0}%
\savestack\thelegend{}%
\setstackgap{S}{0pt}%
\whileboolexpr{test {\ifnumcomp{\thelegcnt}<{101}}}{%
\savestack\thelegend{\stackon{\thelegend}{\textcolor{%
plotcolmax!\thelegcnt!plotcolmin}{\rule{\legendwd}{\dlegend}}}}%
\stepcounter{legcnt}%
}%
\fboxrule#1\relax\fboxsep=0pt\relax\fbox{\thelegend}%
\def\plottick{\rule[.5\dimexpr-\dp\strutbox+\ht\strutbox]{5pt}{%
\fboxrule}}%
\raisebox{.5\dimexpr\dp\strutbox-\ht\strutbox-\fboxrule}{%
\def\stackalignment{l}%
\stackon[\dimexpr\legendht]{\smash{\plottick0}}{\smash{%
\plottick\plotmax\ #2}}%
}%
}}
\begin{document}
\def\cellwd{5pt}
\colorlet{plotcolmax}{blue!90}
\colorlet{plotcolmin}{yellow!80}
\def\legendwd{8pt}
\def\legendht{40pt}
\plotit[1.]{pdq.dat}
~\makelegend[.1pt]{Pa}

\plotit[1.2]{pdq.dat}
~\makelegend[.1pt]{Pa}

\plotit[1.29]{pdq.dat}
~\makelegend[.1pt]{Pa}

\plotit[1.299]{pdq.dat}
~\makelegend[.1pt]{Pa}

\end{document}


• This is close to what I'd want. I'd like a colorbar, and possibly the abillity to add axis'es (with interchangable tik lables)) – Thorbjørn E. K. Christensen Sep 27 '18 at 14:58
• @ThorbjørnE.K.Christensen I might be able to cobble together a colorbar macro, but for axes, I would suggest embedding the \plotit inside some other application like tikz. Nothing I do here supports axis generation. – Steven B. Segletes Sep 27 '18 at 15:00
• Do you want to show an example of how that would be done? That would be amazing !!! – Thorbjørn E. K. Christensen Sep 27 '18 at 15:06
• @ThorbjørnE.K.Christensen I don't use tikz, so I can't guarantee anything there, but I will start looking at a legend macro. – Steven B. Segletes Sep 27 '18 at 15:12
• @ThorbjørnE.K.Christensen \legend capability has been added. – Steven B. Segletes Sep 27 '18 at 15:50

# What I nearly ended up doing

I discovered the feature in gnuplot called plot file matrix with image that does exactly what I want. Then all there's left to do is combine it with pgfplots. To do this in a nice way, I've combined some of marmots answer with gnuplot into a command:

\newcommand{\plotMatrixData}[4]{
%This part Marmot did to find the number of column's and rows, I needed that for niceness
\pgfplotstablegetrowsof{\datatable}
\pgfmathtruncatemacro{\numrows}{\pgfplotsretval}
\pgfplotstablegetcolsof{\datatable}
\pgfmathtruncatemacro{\numcols}{\pgfplotsretval}
%Here's the actual new part
\addplot[matrix plot, mesh/rows=\numrows,mesh/cols=\numcols] gnuplot [raw gnuplot, id=#2] {set datafile separator '#3'; plot '#1' matrix with image};
}


Now one can easily plot a smaller matrix from a file here's a (maybe working) MWE:

\documentclass[border=5pt,tikz]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.15}
\usepackage{pgfplotstable}
\newcommand{\plotMatrixData}[4]{
%This part Marmot did to find the number of column's and rows, I needed that for niceness
\pgfplotstablegetrowsof{\datatable}
\pgfmathtruncatemacro{\numrows}{\pgfplotsretval}
\pgfplotstablegetcolsof{\datatable}
\pgfmathtruncatemacro{\numcols}{\pgfplotsretval}
%Here's the actual new part
\addplot[matrix plot, mesh/rows=\numrows,mesh/cols=\numcols] gnuplot [raw gnuplot, id=#2] {set datafile separator '#3'; plot '#1' matrix with image};
}

\begin{document}
\begin{tikzpicture}
\begin{axis}
\plotMatrixData{d.dat}{d}{,}{comma};
\end{axis}
\end{tikzpicture}
\end{document}


where d.dat could be

1,2
3,4


The problem is if the files become much larger. I wan't to plot multiple really large area heat maps (around 700,000.00 points each) When trying to do this in pdflatex I instantly run out of memory, In lualatex it takes a very long time (23+ minutes and counting) While doing the gnuplotcode directly, plotting takes less than 1 second. So gnuplot is not the bottlenek. I think I'll try something like \tikzexternalize But unless I get a faster method I think I'll give up on LaTeX for creating these figures ;-(