PGFPlots Line of Best Fit Scale and Inversion Error

Question

I am attempting to draw a linear regression line on my graph using pgfplotstable. However, for some reason, it appears to be calculating the regression three orders of magnitude too large and inverted, is this a bug or am I doing something wrong?

My data-set:

lnPa    1/T
6.5723  0.002304
6.7214  0.002273
6.7178  0.002273
6.7117  0.002278
6.7178  0.002278
6.6783  0.002283
6.6490  0.002288
6.6254  0.002294
6.6026  0.002299
6.5820  0.002304
6.5539  0.002309
6.4907  0.002320
6.4281  0.002331
6.3509  0.002347
6.2823  0.002364
6.2066  0.002381
6.1312  0.002381
6.0707  0.002404
6.0113  0.002421
5.8861  0.002445
5.8141  0.002506
5.7236  0.002475
5.6490  0.002494
5.5759  0.002506
5.5134  0.002519
5.3660  0.002545
5.2679  0.002571
5.1761  0.002584
5.0876  0.002597
5.0239  0.002611
4.9628  0.002625
4.8283  0.002646
4.7791  0.002660

It plots a graph like this without the regression line:

However, when I add in the line of best fit:

The figure for this is as below:

\begin{figure}[H]
\centering
\begin{tikzpicture}
\begin{axis}[legend pos=north east,anchor=west, xlabel={$T^{-1}/ K^{-1}$}, ylabel={$\ln P*_a$}]
\addplot table [only marks, x=1/T,y=lnPa]{GraphData.txt};
\addplot [no markers, thick, red] table [y={create col/linear regression={y=lnPa}}]{GraphData.txt};
%\addlegendentry{$\dfrac{dy}{dx} = \pgfplotstableregressiona$}
%\addlegendentry{$y_{intercept} = \pgfplotstableregressionb$}
\end{axis}
\end{tikzpicture}
\caption{Graph to show the relationship between the natural log of pressure and the inverse of temperature}
\label{fig:ResultsGraph}
\end{figure}

Can anyone spot what's going on here?

Answer 1

Here is the solution:

\documentclass{article}
\usepackage{filecontents}
\usepackage{tikz,pgfplots}
\usepackage{pgfplotstable} 
\begin{filecontents}{GraphData.txt}
   lnPa    1/T
6.5723  0.002304
6.7214  0.002273
6.7178  0.002273
6.7117  0.002278
6.7178  0.002278
6.6783  0.002283
6.6490  0.002288
6.6254  0.002294
6.6026  0.002299
6.5820  0.002304
6.5539  0.002309
6.4907  0.002320
6.4281  0.002331
6.3509  0.002347
6.2823  0.002364
6.2066  0.002381
6.1312  0.002381
6.0707  0.002404
6.0113  0.002421
5.8861  0.002445
5.8141  0.002506
5.7236  0.002475
5.6490  0.002494
5.5759  0.002506
5.5134  0.002519
5.3660  0.002545
5.2679  0.002571
5.1761  0.002584
5.0876  0.002597
5.0239  0.002611
4.9628  0.002625
4.8283  0.002646
4.7791  0.002660
\end{filecontents}


\begin{document}

\begin{tikzpicture}
\begin{axis}[legend pos=north east,anchor=west, xlabel={$T^{-1}/ K^{-1}$}, ylabel={$\ln P*_a$}]
\addplot table [only marks, x={1/T},y={lnPa}]{GraphData.txt};
\addplot [thick, red] table[x={1/T},
    y={create col/linear regression={y={lnPa}}}
] % compute a linear regression from the input table
{GraphData.txt};
%\addlegendentry{$\dfrac{dy}{dx} = \pgfplotstableregressiona$}
%\addlegendentry{$y_{intercept} = \pgfplotstableregressionb$}
\end{axis}
\end{tikzpicture}
\end{document}

Result:

I just realized that it was plotting the axes in deferent order. The reason was that your x axis numbers was at the second column and so you have to give the x axis name of the column before ask for linear regression of y.

PS: The truth is that the image is "stolen" from @StefanPinnow that answered independent from me at the same time and probably knew the reason before I discover it today.