\pgfplotstablegetelem problem

Question

I am trying to access values from a file one by one, and using the following code to do it:

\nextgroupplot[
    width=0.3*\plotwidth,
]
    \foreach \i in {1,...,10}{
        \foreach \j in {0,...,9}{
            \ifnum\i>\j
                \pgfplotstablegetelem{\i}{\j}\of{\first};
                %\let\param\pgfplotsretval;
                %\node at (axis cs:1.5, 0.5) {\pgfplotsretval};
                \addplot [draw=none, mark=, fill=blue, fill opacity=1] coordinates {(0.5+\j, -0.5+\i)} node[pos=0.1] {\pgfplotsretval};
            \else
            \fi         
        }
}

Unfortunately, it does not work, and I fail to see the problem. Interestingly, when I use

\node at (axis cs:1.5, 0.5) {\pgfplotsretval};

it works -- almost, since it only gives me the first digit of the numbers in the table.

P.S. By the way, I am not using this to just put numbers in a grid. It is a debugging step, I will eventually use the values to draw colours from a \colormap.

MWE:

\begin{filecontents*}{data.csv}
1   2   3   4   5   6   7   8   9   10
0.1 0   0   0   0   0   0   0   0   0
0.05625 0.012499999999999999    0   0   0   0   0   0   0   0
0.05185185185185186 0.008101851851851851    0.003703703703703704    0   0   0   0   0   0   0
0.05078125  0.007031249999999999    0.0026331018518518517   0.0015625   0   0   0   0   0   0
0.0504  0.00665 0.002251851851851852    0.00118125  0.0008000000000000001   0   0   0   0   0
0.05023148148148148 0.006481481481481481    0.0020833333333333333   0.0010127314814814816   0.0006314814814814816   0.00046296296296296303  0   0   0   0
0.05014577259475219 0.006395772594752186    0.0019976244466040384   0.0009270225947521866   0.0005457725947521867   0.0003772540762336681   0.0002915451895043732   0   0   0
0.050097656250000004    0.006347656249999999    0.001949508101851852    0.00087890625   0.00049765625   0.0003291377314814815   0.00024342884475218656  0.00019531249999999998  0   0
0.050068587105624146    0.006318587105624142    0.0019204389574759945   0.0008498371056241427   0.00046858710562414275  0.00030006858710562417  0.00021435970037632926  0.00016624335562414266  0.00013717421124828533  0
0.050050000000000004    0.006299999999999999    0.0019018518518518518   0.0008312500000000001   0.0004500000000000001   0.0002814814814814815   0.00019577259475218658  0.00014765625   0.00011858710562414267  0.0001
\end{filecontents*}

\documentclass[margin=5mm]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.8}
\usepackage{pgfplotstable}
\usepgfplotslibrary{groupplots}

\definecolor{color1}{RGB}{202,0,32}
\definecolor{color2}{RGB}{244,165,130}
\definecolor{color3}{RGB}{146,197,222}
\definecolor{color4}{RGB}{5,113,176}

\def \plotwidth {510.0pt}

\begin{document}
\pgfplotstableread[col sep=tab]{data/first_order.dat}{\first}

\begin{tikzpicture}
\begin{groupplot}[
    group style = {
        group size = 3 by 1,
        horizontal sep = 0pt,
        yticklabels at=edge left,
    },
    height = 150pt,
    width = \plotwidth,
    xmin=0, xmax=10,
    ymin=0, ymax=10,
    xtick = {0.5, 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, 7.5, 8.5, 9.5},
    ytick = {0.5, 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, 7.5, 8.5, 9.5},
]
\nextgroupplot[
    width=0.3*\plotwidth,
]
    \foreach \i in {1,...,5}{
        \foreach \j in {0,...,3}{
            \ifnum\i>\j
                \pgfplotstablegetelem{\i}{\j}\of{\first};
                \addplot [draw=none, mark=, fill=blue, fill opacity=1] coordinates {(0.5+\j, -0.5+\i)} node[pos=0.1] {\pgfplotsretval};
            \else
            \fi         
        }
    }
\nextgroupplot[
    width=0.3*\plotwidth
]
\nextgroupplot[
    width=0.3*\plotwidth
]
  \end{groupplot}
\end{tikzpicture}
\end{document}

Answer 1

I had to make a number of changes to get your MWE to run (tabs got converted to spaces). I also got rid of all the groupplots, as getting one plot to work was difficult enough. I'm not sure what the \addplots were supposed to do besides position the nodes.

Anyway, the solution was to use \pgfplotsextra for the entire loop. Otherwise by the time the node was drawn, \i was always 5 and \j was always 3. See also \pgfplotsforeachungrouped and \pgfplotsinvokeforeach.

\begin{filecontents*}{data.csv}
1,  2,  3,  4,  5,  6,  7,  8,  9,  10
0.1, 0,  0,  0,  0,  0,  0,  0,  0,  0
0.05625, 0.012499999999999999,   0,  0,  0,  0,  0,  0,  0,  0
0.05185185185185186, 0.008101851851851851,   0.003703703703703704,   0,  0,  0,  0,  0,  0,  0
0.05078125, 0.007031249999999999,   0.0026331018518518517,  0.0015625,  0,  0,  0,  0,  0,  0
0.0504, 0.00665, 0.002251851851851852, 0.00118125, 0.0008000000000000001,  0,  0,  0,  0,  0
0.05023148148148148, 0.006481481481481481,  0.0020833333333333333,  0.0010127314814814816,  0.0006314814814814816,  0.00046296296296296303, 0, 0, 0, 0
0.05014577259475219, 0.006395772594752186,  0.0019976244466040384,  0.0009270225947521866,  0.0005457725947521867,  0.0003772540762336681,  0.0002915451895043732, 0,  0,  0
0.050097656250000004, 0.006347656249999999, 0.001949508101851852, 0.00087890625, 0.00049765625, 0.0003291377314814815, 0.00024342884475218656, 0.00019531249999999998, 0, 0
0.050068587105624146, 0.006318587105624142, 0.0019204389574759945, 0.0008498371056241427, 0.00046858710562414275, 0.00030006858710562417, 0.00021435970037632926, 0.00016624335562414266, 0.00013717421124828533, 0
0.050050000000000004, 0.006299999999999999, 0.0019018518518518518, 0.0008312500000000001, 0.0004500000000000001, 0.0002814814814814815, 0.00019577259475218658, 0.00014765625, 0.00011858710562414267, 0.0001
\end{filecontents*}

\documentclass[margin=5mm]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.8}
\usepackage{pgfplotstable}
\usepgfplotslibrary{groupplots}

\definecolor{color1}{RGB}{202,0,32}
\definecolor{color2}{RGB}{244,165,130}
\definecolor{color3}{RGB}{146,197,222}
\definecolor{color4}{RGB}{5,113,176}

\def \plotwidth {510.0pt}

\begin{document}
\pgfplotstableread[col sep=comma]{data.csv}{\first}
%\pgfplotstabletypeset{\first}

\begin{tikzpicture}
\begin{axis}[
    height = 150pt,
    width = 5in,
    xmin=0, xmax=10,
    ymin=0, ymax=10,
    xtick = {0.5, 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, 7.5, 8.5, 9.5},
    ytick = {0.5, 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, 7.5, 8.5, 9.5},
]
\pgfplotsextra{
    \foreach \i in {1,...,5}{
        \foreach \j in {0,...,3}{
            \ifnum\i>\j\relax
                \pgfplotstablegetelem{\i}{\j}\of\first
                \node at (axis cs: 0.5+\j, -0.5+\i) {\pgfplotsretval};
            \else
            \fi         
        }
    }
}
\end{axis}
\end{tikzpicture}
\end{document}