[Tex/LaTex] How to make a nice legend for a histogram with pgfplots

legendpgfplots

I am trying to make a histogram with the fitted curve plotted on it. Here's the mwe:

 \documentclass[a4paper]{scrartcl}
    \usepackage{tikz}
    \usepackage{pgfplots,pgfplotstable}
    \usepackage{filecontents}
    \pgfplotsset{compat=1.10}
    \usepackage[active,tightpage]{preview}
    \setlength\PreviewBorder{2pt}
    \newcommand{\plots}{0.611201}
    \newcommand{\plotm}{2.19882}
    \begin{filecontents}{data.dat}
    2 0.0629921259843
    3 0.0236220472441
    4 0.0314960629921
    5 0.125984251969
    6 0.0629921259843
    7 0.102362204724
    8 0.110236220472
    9 0.0551181102362
    10 0.0629921259843
    11 0.0314960629921
    12 0.0236220472441
    13 0.0314960629921
    14 0.0629921259843
    15 0.0551181102362
    16 0.0393700787402
    17 0.0472440944882
    18 0.00787401574803
    19 0.0393700787402
    24 0.00787401574803
    27 0.00787401574803
    33 0.00787401574803
    \end{filecontents}
    \begin{document}
    \begin{preview}

    \begin{tikzpicture}
    \begin{axis}[
    yticklabel style={/pgf/number format/fixed},
    scaled y ticks = false,
    minor y tick num={1},
    xtick pos=left,
    legend cell align = left,
    legend style={draw=none},
    xlabel = {group size},
    ylabel = {ratio}
    ]
    \addplot[blue,ybar,fill, fill opacity=0.3, bar width = 0.8,] table {data.dat};
    \addplot[red, line width = 1,domain=1:40,samples=100] {1/(x*sqrt(2*pi)*\plots)*exp(-(ln(x)-\plotm)^2/(2*\plots^2))};
    \legend{empirical,lognormal fit}
    \end{axis}
    \end{tikzpicture}
    \end{preview}
    \end{document}

enter image description here

As you can see, the legend is not really good. How can I change the legend so it looks more like this?

enter image description here

Best Answer

There are a couple of ways of solving this. One way is to move the ybar option from the \addplot to the axis. The same key means slightly different things in the two locations, in the axis it refers to /pgfplots/ybar, while in the \addplot it refers to /tikz/ybar. It would appear that these lead to different behaviours for the legends, though I have not looked at precisely how they're defined.

Of course, when you add ybar to the axis, it will affect all \addplots, so you must also add sharp plot to the line plot. sharp plot is the default style for addplot, it draws a line with markers by default.

Result and complete code first, second option below:

enter image description here

\documentclass[border=5mm]{standalone}
\usepackage{tikz}
\usepackage{pgfplots,pgfplotstable}
\usepackage{filecontents}
\pgfplotsset{compat=1.10}
\newcommand{\plots}{0.611201}
\newcommand{\plotm}{2.19882}
\begin{filecontents}{data.dat}
2 0.0629921259843
3 0.0236220472441
4 0.0314960629921
5 0.125984251969
6 0.0629921259843
7 0.102362204724
8 0.110236220472
9 0.0551181102362
10 0.0629921259843
11 0.0314960629921
12 0.0236220472441
13 0.0314960629921
14 0.0629921259843
15 0.0551181102362
16 0.0393700787402
17 0.0472440944882
18 0.00787401574803
19 0.0393700787402
24 0.00787401574803
27 0.00787401574803
33 0.00787401574803
\end{filecontents}
\begin{document}
\begin{tikzpicture}
\begin{axis}[
yticklabel style={/pgf/number format/fixed},
scaled y ticks = false,
minor y tick num={1},
xtick pos=left,
legend cell align = left,
legend style={draw=none},
xlabel = {group size},
ylabel = {ratio},
ybar
]
\addplot[blue,ybar,fill, fill opacity=0.3, bar width = 0.8] table {data.dat};
\addplot[sharp plot,red, line width = 1,domain=1:40,samples=100,line legend] {1/(x*sqrt(2*pi)*\plots)*exp(-(ln(x)-\plotm)^2/(2*\plots^2))};
\legend{empirical,lognormal fit}
\end{axis}
\end{tikzpicture}
\end{document}

Second option

Another way is to simply add area legend to the options of the \addplot command for the ybar plot. This tells pgfplots to create a filled rectangle as the legend entry, instead of just a line, as in the prefered example. You can also use ybar legend instead of area legend, which will make it like in the first example. You can find the definitions of how the legend entries are created in the manual.

enter image description here

\documentclass[border=5mm]{standalone}
\usepackage{tikz}
\usepackage{pgfplots,pgfplotstable}
\usepackage{filecontents}
\pgfplotsset{compat=1.10}
\newcommand{\plots}{0.611201}
\newcommand{\plotm}{2.19882}
\begin{filecontents}{data.dat}
2 0.0629921259843
3 0.0236220472441
4 0.0314960629921
5 0.125984251969
6 0.0629921259843
7 0.102362204724
8 0.110236220472
9 0.0551181102362
10 0.0629921259843
11 0.0314960629921
12 0.0236220472441
13 0.0314960629921
14 0.0629921259843
15 0.0551181102362
16 0.0393700787402
17 0.0472440944882
18 0.00787401574803
19 0.0393700787402
24 0.00787401574803
27 0.00787401574803
33 0.00787401574803
\end{filecontents}
\begin{document}
\begin{tikzpicture}
\begin{axis}[
yticklabel style={/pgf/number format/fixed},
scaled y ticks = false,
minor y tick num={1},
xtick pos=left,
legend cell align = left,
legend style={draw=none},
xlabel = {group size},
ylabel = {ratio}
]
\addplot[blue,ybar,fill, fill opacity=0.3, bar width = 0.8,area legend] table {data.dat};
\addplot[red, line width = 1,domain=1:40,samples=100] {1/(x*sqrt(2*pi)*\plots)*exp(-(ln(x)-\plotm)^2/(2*\plots^2))};
\legend{empirical,lognormal fit}
\end{axis}
\end{tikzpicture}
\end{document}

Third option (dealing with alignment issues)

As can be seen, in the first option, the legend for the histogram is misaligned. We can fix this by overriding the default behavior of ybar legend. The default behavior (see manual) is

\pgfplotsset{
/pgfplots/xbar legend/.style={
/pgfplots/legend image code/.code={%
\draw[##1,/tikz/.cd,bar width=3pt,yshift=-0.2em,bar shift=0pt]
plot coordinates {(0cm,0.8em) (2*\pgfplotbarwidth,0.6em)};},
},
}

Here's an example with the complete code for a much nicer looking ybar legend

enter image description here

\documentclass[border=5mm]{standalone}
\usepackage{tikz}
\usepackage{pgfplots,pgfplotstable}
\usepackage{filecontents}
\pgfplotsset{compat=1.10}
\newcommand{\plots}{0.611201}
\newcommand{\plotm}{2.19882}
\begin{filecontents}{data.dat}
2 0.0629921259843
3 0.0236220472441
4 0.0314960629921
5 0.125984251969
6 0.0629921259843
7 0.102362204724
8 0.110236220472
9 0.0551181102362
10 0.0629921259843
11 0.0314960629921
12 0.0236220472441
13 0.0314960629921
14 0.0629921259843
15 0.0551181102362
16 0.0393700787402
17 0.0472440944882
18 0.00787401574803
19 0.0393700787402
24 0.00787401574803
27 0.00787401574803
33 0.00787401574803
\end{filecontents}
\pgfplotsset{
/pgfplots/ybar legend/.style={
/pgfplots/legend image code/.code={%
\draw[##1,/tikz/.cd,bar width=0.1cm,yshift=-0.2em,bar shift=0.5*\pgfplotbarwidth]
plot coordinates {(0.5*\pgfplotbarwidth,0.6em) (2.5*\pgfplotbarwidth,0.4em) (4.5*\pgfplotbarwidth,0.2em)};},
}
}
\begin{document}
\begin{tikzpicture}
\begin{axis}[
yticklabel style={/pgf/number format/fixed},
scaled y ticks = false,
minor y tick num={1},
xtick pos=left,
legend cell align = left,
legend style={draw=none},
xlabel = {group size},
ylabel = {ratio}
]
\addplot[blue,ybar,fill, fill opacity=0.3, bar width = 0.8,ybar legend] table {data.dat};
\addplot[red, line width = 1,domain=1:40,samples=100] {1/(x*sqrt(2*pi)*\plots)*exp(-(ln(x)-\plotm)^2/(2*\plots^2))};
\legend{empirical,lognormal fit}
\end{axis}
\end{tikzpicture}
\end{document}

Related Solutions

[Tex/LaTex] plotting two time series with bounds

This happens because PGFPlots only uses one "stack" per axis: You're stacking the second confidence interval on top of the first. The easiest way to fix this is probably to use the approach described in "Is there an easy way of using line thickness as error indicator in a plot?": After plotting the first confidence interval, stack the upper bound on top again, using stack dir=minus. That way, the stack will be reset to zero, and you can draw the second confidence interval in the same fashion as the first:

\documentclass{standalone}
\usepackage{pgfplots, tikz}

\usepackage{pgfplotstable}

\pgfplotstableread{
temps   y_h y_h__inf    y_h__sup    y_f y_f__inf    y_f__sup    

1   0.237340    0.135170    0.339511    0.237653    0.135482    0.339823    
2   0.561320    0.422007    0.700633    0.165871    0.026558    0.305184    
3   0.694760    0.534205    0.855314    0.074856    -0.085698   0.235411    
4   0.728306    0.560179    0.896432    0.003361    -0.164765   0.171487    
5   0.711710    0.544944    0.878477    -0.044582   -0.211349   0.122184    
6   0.671241    0.511191    0.831291    -0.073347   -0.233397   0.086703    
7   0.621177    0.471219    0.771135    -0.088418   -0.238376   0.061540    
8   0.569354    0.431826    0.706882    -0.094382   -0.231910   0.043146    
9   0.519973    0.396571    0.643376    -0.094619   -0.218022   0.028783    
10  0.475121    0.366990    0.583251    -0.091467   -0.199598   0.016664    
}{\table}

\begin{document}
\begin{tikzpicture}

    \begin{axis}
    % y_h confidence interval
    \addplot [stack plots=y, fill=none, draw=none, forget plot]   table [x=temps, y=y_h__inf]   {\table} \closedcycle;
    \addplot [stack plots=y, fill=gray!50, opacity=0.4, draw opacity=0, area legend]   table [x=temps, y expr=\thisrow{y_h__sup}-\thisrow{y_h__inf}]   {\table} \closedcycle;
    % subtract the upper bound so our stack is back at zero
    \addplot [stack plots=y, stack dir=minus, forget plot, draw=none] table [x=temps, y=y_h__sup] {\table};

    % y_f confidence interval
    \addplot [stack plots=y, fill=none, draw=none, forget plot]   table [x=temps, y=y_f__inf]   {\table} \closedcycle;
    \addplot [stack plots=y, fill=gray!50, opacity=0.4, draw opacity=0, area legend]   table [x=temps, y expr=\thisrow{y_f__sup}-\thisrow{y_f__inf}]   {\table} \closedcycle;

    % the line plots (y_h and y_f)    
    \addplot [stack plots=false, very thick,smooth,blue]  table [x=temps, y=y_h]   {\table};
    \addplot [stack plots=false, very thick,smooth,blue]  table [x=temps, y=y_f]   {\table};
    \end{axis}

\end{tikzpicture}
\end{document}

[Tex/LaTex] How to make the legend box transparent in pgfplots

You can add fill=none to the legend style key as in this approach.

\documentclass[11pt]{article}
\usepackage[T1]{fontenc}
\usepackage{pgfplots}

\pgfplotsset{compat=1.9}

\begin{document}
  \begin{tikzpicture}
    \begin{axis}[
      legend style={fill=none}
    ]
      \addplot {x};
      \addlegendentry{$x$};
    \end{axis}
  \end{tikzpicture}
\end{document}

enter image description here

Best Answer

Second option

Third option (dealing with alignment issues)

Related Solutions

[Tex/LaTex] plotting two time series with bounds

[Tex/LaTex] How to make the legend box transparent in pgfplots

Related Question