PGFPLOTS Histogram: Customizing X-Axis Labels

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Discussion Overview

The discussion revolves around customizing the x-axis labels of a histogram created using the pgfplots package in LaTeX. Participants explore how to adjust the labeling to show boundaries between intervals instead of labeling the intervals themselves, which some find confusing. The conversation includes technical aspects of histogram plotting, potential solutions, and considerations regarding data point placement.

Discussion Character

  • Technical explanation, Debate/contested, Exploratory

Main Points Raised

  • One participant expresses a desire to change the x-axis labels from interval labels to boundary labels for clarity.
  • Another participant provides a screenshot to illustrate the current labeling issue and seeks confirmation on their desired outcome.
  • Some participants suggest that while manual computation of boundary values is necessary, the pgfmathparser could assist with calculations.
  • There is a suggestion to remove "ybar interval" and use "xtick=data" to clarify the type of plot desired.
  • Concerns are raised about data points falling directly on boundaries, which could lead to ambiguity regarding bin assignments, referencing statistical guidelines.
  • One participant notes that pgfplots documentation indicates that bins include the left boundary and exclude the right boundary, which should mitigate ambiguity.
  • Another participant mentions a preference for assigning bins on "nice coordinates" for clarity.

Areas of Agreement / Disagreement

Participants express varying opinions on the best approach to labeling and bin assignment, with some agreeing on the need for boundary labeling while others highlight potential issues with data point placement. The discussion remains unresolved regarding the optimal method for achieving the desired labeling without ambiguity.

Contextual Notes

Participants reference statistical guidelines regarding data point placement on boundaries and the implications for histogram interpretation. There is mention of specific behaviors of pgfplots regarding bin boundaries, which may influence how participants approach their histogram customization.

Ackbach
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Warning: requires the tikz and pgfplots packages.

I've got my histogram almost where I want it:

Code: 
\begin{center}
\begin{tikzpicture}
\begin{axis}[
  tiny,
  width=6in,
  ymin=0,
  ybar interval,
  ]
  \addplot+[hist={bins=10,density}]
    table[row sep=\\,y index=0] {
    	data \\
      565 \\ 786 \\ 870 \\ 923 \\ 948 \\ 951 \\ 964 \\ 968 \\
      997 \\1007 \\1013 \\1037 \\1040 \\1051 \\1056 \\1080 \\
     1088 \\1090 \\1102 \\1103 \\1104 \\1120 \\1151 \\1159 \\
     1165 \\1185 \\1189 \\1207 \\1216 \\1233 \\1251 \\1256 \\
     1261 \\1292 \\1312 \\1317 \\1347 \\1358 \\1385 \\1416 \\
     1477 \\1500 \\1514 \\1567 \\1592 \\1588 \\1615 \\1713 \\
     2325 \\3168 \\};
\end{axis}
\end{tikzpicture}
\end{center}

The one thing I want to change is where the $x$-axis labels are showing up. Instead of labeling the intervals (which I think is extremely confusing and unhelpful unless you give the range, which won't fit here), I want to label the boundaries between the intervals. How can I get pgfplots to do that? Thanks!
 
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Ackbach said:
Warning: requires the tikz and pgfplots packages.

I've got my histogram almost where I want it:

Code: 
\begin{center}
\begin{tikzpicture}
\begin{axis}[
  tiny,
  width=6in,
  ymin=0,
  ybar interval,
  ]
  \addplot+[hist={bins=10,density}]
    table[row sep=\\,y index=0] {
        data \\
      565 \\ 786 \\ 870 \\ 923 \\ 948 \\ 951 \\ 964 \\ 968 \\
      997 \\1007 \\1013 \\1037 \\1040 \\1051 \\1056 \\1080 \\
     1088 \\1090 \\1102 \\1103 \\1104 \\1120 \\1151 \\1159 \\
     1165 \\1185 \\1189 \\1207 \\1216 \\1233 \\1251 \\1256 \\
     1261 \\1292 \\1312 \\1317 \\1347 \\1358 \\1385 \\1416 \\
     1477 \\1500 \\1514 \\1567 \\1592 \\1588 \\1615 \\1713 \\
     2325 \\3168 \\};
\end{axis}
\end{tikzpicture}
\end{center}

The one thing I want to change is where the $x$-axis labels are showing up. Instead of labeling the intervals (which I think is extremely confusing and unhelpful unless you give the range, which won't fit here), I want to label the boundaries between the intervals. How can I get pgfplots to do that? Thanks!
can you post a picture of what it looks like and what you want?
 
Sure. Here's a screenshot of a histogram produced by code very similar to what I posted.

View attachment 1947

Now you see the numbers on the horizontal axis - they're lined up with the intervals, and I find that rather ambiguous. I want to have numbers (they might be different from the ones currently showing) marking the boundaries of the intervals, not the intervals themselves, and I want the numbers aligned under the boundaries.

Does that further clarify what I'm after?
 

Attachments

  • Histogram.png
    Histogram.png
    2.5 KB · Views: 178
Hmm, you mean something like this?

View attachment 1948

[LATEXS]\documentclass{article}
\usepackage{tikz}
\usepackage{pgfplots}

\begin{document}
\begin{tikzpicture}
\begin{axis}[
width=6in,
ymin=0,
xtick=data,
]
\addplot[
ybar interval,
draw=black!60,
fill=blue!20,
mark=none,
] coordinates {
(750, 0.02) (1000, 0.16) (1250, 0.42) (1500, 0.24) (1750, 0.12) (2000, 0)
(2250, 0) (2500, 0.02) (2750, 0) (3000, 0) (3250, 0.02) (3500, 0.02)
};
\end{axis}
\end{tikzpicture}
\end{document}[/LATEXS]
 

Attachments

  • tikz_histogram.png
    tikz_histogram.png
    2.7 KB · Views: 170
Yes! Very nice, thank you! I don't suppose you can get TiKZ to to that automatically? (I know, I'm only asking for the moon, here.) I see you have to compute the values yourself, which is fine. But if TiKZ could compute those for me, that would be AWESOME.
 
Ackbach said:
Yes! Very nice, thank you! I don't suppose you can get TiKZ to to that automatically? (I know, I'm only asking for the moon, here.) I see you have to compute the values yourself, which is fine. But if TiKZ could compute those for me, that would be AWESOME.

The pgfmathparser can do calculations. Check out the manual.
 
Ackbach said:
Yes! Very nice, thank you! I don't suppose you can get TiKZ to to that automatically? (I know, I'm only asking for the moon, here.) I see you have to compute the values yourself, which is fine. But if TiKZ could compute those for me, that would be AWESOME.

Mmmmh, suppose you remove the "ybar interval" so TikZ won't be confused which type of plot you want, and add "xtick=data" to indicate you want to use the x coordinates of the data as labels...

View attachment 1950

[LATEXS]\documentclass{article}
\usepackage{tikz, pgfplots}
\begin{document}
\begin{tikzpicture}
\begin{axis}[ tiny,
width=6in,
xtick=data,
ymin=0 ]
\addplot+[
hist={ bins=10, density },
fill=blue!20,
mark=none,
] table[ row sep=\\, y index=0 ] {
data \\ 565 \\ 786 \\ 870 \\ 923 \\ 948 \\ 951 \\ 964 \\ 968 \\
997 \\1007 \\1013 \\1037 \\1040 \\1051 \\1056 \\1080 \\
1088 \\1090 \\1102 \\1103 \\1104 \\1120 \\1151 \\1159 \\
1165 \\1185 \\1189 \\1207 \\1216 \\1233 \\1251 \\1256 \\
1261 \\1292 \\1312 \\1317 \\1347 \\1358 \\1385 \\1416 \\
1477 \\1500 \\1514 \\1567 \\1592 \\1588 \\1615 \\1713 \\
2325 \\3168 \\
};
\end{axis}
\end{tikzpicture}
\end{document}[/LATEXS]
 

Attachments

  • tikz_histogram2.png
    tikz_histogram2.png
    2.8 KB · Views: 156
I like Serena said:
Mmmmh, suppose you remove the "ybar interval" so TikZ won't be confused which type of plot you want, and add "xtick=data" to indicate you want to use the x coordinates of the data as labels...

View attachment 1950

[LATEXS]\documentclass{article}
\usepackage{tikz, pgfplots}
\begin{document}
\begin{tikzpicture}
\begin{axis}[ tiny,
width=6in,
xtick=data,
ymin=0 ]
\addplot+[
hist={ bins=10, density },
fill=blue!20,
mark=none,
] table[ row sep=\\, y index=0 ] {
data \\ 565 \\ 786 \\ 870 \\ 923 \\ 948 \\ 951 \\ 964 \\ 968 \\
997 \\1007 \\1013 \\1037 \\1040 \\1051 \\1056 \\1080 \\
1088 \\1090 \\1102 \\1103 \\1104 \\1120 \\1151 \\1159 \\
1165 \\1185 \\1189 \\1207 \\1216 \\1233 \\1251 \\1256 \\
1261 \\1292 \\1312 \\1317 \\1347 \\1358 \\1385 \\1416 \\
1477 \\1500 \\1514 \\1567 \\1592 \\1588 \\1615 \\1713 \\
2325 \\3168 \\
};
\end{axis}
\end{tikzpicture}
\end{document}[/LATEXS]

Better and better! The only catch with this is that according to my statistics book, it's not considered a good idea to have any data points fall directly on a boundary. Then it's confusing which bin that data point is supposed to be in. Now, if in the plot you gave, that only happens at the endpoints (possibly only one?), then I suppose that wouldn't be ambiguous. And if it does happen somewhere in the middle, maybe I could mitigate that by changing the number of bins. Does that sound reasonable?
 
Ackbach said:
Better and better! The only catch with this is that according to my statistics book, it's not considered a good idea to have any data points fall directly on a boundary. Then it's confusing which bin that data point is supposed to be in. Now, if in the plot you gave, that only happens at the endpoints (possibly only one?), then I suppose that wouldn't be ambiguous. And if it does happen somewhere in the middle, maybe I could mitigate that by changing the number of bins. Does that sound reasonable?

Pgfplots documentation says that each bin includes the left boundary and excludes the right boundary so there is no ambiguity. That is an interval of the type [a,b). As far as I'm concerned that is pretty standard.
That is with the exception of the rightmost bin that does include the right boundary, which is not ambiguous.
In this particular histogram both the leftmost bin and the rightmost bin have 1 data point on the boundary simply because the bins are bounded this way. That should be okay since there is no ambiguity.
Btw, my own preference is to assign bins on nice coordinates, as I did in the my first response.
 
  • #10
I like Serena said:
Pgfplots documentation says that each bin includes the left boundary and excludes the right boundary so there is no ambiguity. That is an interval of the type [a,b). As far as I'm concerned that is pretty standard.
That is with the exception of the rightmost bin that does include the right boundary, which is not ambiguous.
In this particular histogram both the leftmost bin and the rightmost bin have 1 data point on the boundary simply because the bins are bounded this way. That should be okay since there is no ambiguity.
Btw, my own preference is to assign bins on nice coordinates, as I did in the my first response.

Gotcha. Thanks very much, I like Serena and dwsmith! You've been very helpful.
 

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