ENH: Added a `PercentFormatter` class to `matplotlib.ticker` #6251

madphysicist · Mar 30, 2016

This is suitable for formatting axes labels as percentages. It has some nice features like being able to convert from arbitrary data scales to percents, a customizable percent symbol and either automatic or manual control over the decimal points.

The original motivation came from my own work as well as these two Stack Overflow questions:

madphysicist · Mar 30, 2016

@mdboom While I realize that you have a script to do this, it is really disconcerting to see your name pop up fractions of a second after I create a PR :)

precision

Percent

This needs to match the name in the signature (i.e., 'max' needs to be the kwarg).

madphysicist · Mar 30, 2016

I am not familiar enough with Python 2.7 to immediately understand why the following is not working:

s = '{x:0.{decimals}f}'.format(x=x, decimals=decimals)

Are nested formats not allowed?

I think people will rarely want to specify max, so I would put it after the decimals kwarg.

I disagree. The most common parameter to modify would be max. This is intended for data going from 0 to 1, or as in the case of the SO question, from 0 to 5. I would expect the decimals argument to generally remain None assuming I have done a decent job with the automated version.

I like to use parentheses to make expressions like this clearer; or multiply by 100 first.

Doing both. I agree that it looks awkward.

efiring · Mar 30, 2016

There are so many cleanup changes here that I recommend breaking this into two PRs: one for the cleanups, and a second one for the new feature.

madphysicist · Mar 30, 2016

No problem with that. Is there an easy way to do that without closing this PR?

Oops!

QuLogic · Mar 30, 2016

@mdboom While I realize that you have a script to do this, it is really disconcerting to see your name pop up fractions of a second after I create a PR :)

That's https://waffle.io/

No problem with that. Is there an easy way to do that without closing this PR?

Create a new branch starting on this one, rebase it to include only cleanup, and open a new PR for it. When that's merged, rebase this one on top of master and drop all the cleanup from here.

efiring · Mar 30, 2016

I think you would make a separate branch on your repo for the cleanups, and make a PR from that. Then, on your pctFormatter branch, isolate the PercentFormatter part with additional commits, and use 'git rebase -i' to squash it down to a single commit. Force-push that to your github repo, and it will replace the present commits in the present PR.

madphysicist · Mar 31, 2016

I did the split (#6253) and fixed the Py2.7 error. Turns out Py3 automatically converts acceptable format precisions into an int. Py2 does not.

The only potentially unrelated change I kept here was moving __all__ to the top.

madphysicist · Mar 31, 2016

Metabolized the docs of EngFormatter.format_eng from #6253 into this commit to get rid of sphinx errors.

madphysicist · Apr 1, 2016

I think that this PR is complete (ready for further review). Same goes for #6253.

The failure in Appveyor is the sporadic image comparison failure. It is not related to the code I added as far as I can tell.

madphysicist · Apr 7, 2016

Squawk.

mdboom · Apr 7, 2016

Cc: @efiring.

efiring · Apr 7, 2016

In reading the new code, I find that I waste a lot of time trying to figure out what d really is. I am comfortable with short variable names like x when their meaning is obvious from the context; but d is not obvious here--especially since some places it is in unscaled data units, and other places in percent. So maybe use dspan or xspan, and pcspan, or something like that? And maybe xmax instead of mx? Readability matters, both in the tests and in the active code.

madphysicist · Apr 8, 2016

I changed max to xmax throughout, and changed d to display_range and scaled_range as appropriate. I think that does make a big improvement to readability.

On a side-note, I got d from OldScalarFormatter, originally thinking to reuse its pprint method. I don't think that d needs to be changed at this point, but it is a possibility. d also appears in at least one of the Locators.

pep-8 failure here: line too long. You could use parentheses; or you could use

    for case in test_cases:
        yield (_percent_format_helper,) + case

I haven't tested, but I think that would work and would be more readable.
Maybe I would use args and test_args instead of case and test_cases.

efiring · Apr 8, 2016

In addition to the pep-8 failure noted above there is a real failure that I have not tracked down (probably you will spot it instantly). Once those are taken care of, I think this will be functionally ready. It's a nice contribution. You could neaten it up by rebasing to squash the commits.

madphysicist · Apr 8, 2016

I went with

for case in test_cases:
    yield (_percent_format_helper, *case)

and also fixed the other stupid typo. Will push with squash soon.

madphysicist · Apr 8, 2016

And now I know why I should have listened the first time.

madphysicist · Apr 8, 2016

I don't think the Travis failure is related to my code.

efiring · Apr 8, 2016

Thank you, @madphysicist!

madphysicist · Apr 8, 2016

No problem. Thanks for looking over and accepting my PR!

mdboom added the needs_review label Mar 30, 2016

efiring commented on an outdated diff Mar 30, 2016

View full outdated diff
lib/matplotlib/ticker.py

+:class:`EngFormatter`

+ Format labels in engineering notation

+

+:class:`PerentFormatter`

efiring Mar 30, 2016
Owner

Percent

madphysicist referenced this pull request Mar 31, 2016
Merged
MAINT: Updates to formatters in `matplotlib.ticker` #6253

madphysicist changed the title from Added a PercentFormatter class to `matplotlib.ticker` to ENH: Added a PercentFormatter class to `matplotlib.ticker` Mar 31, 2016

madphysicist changed the title from ENH: Added a PercentFormatter class to `matplotlib.ticker` to ENH: Added a `PercentFormatter` class to `matplotlib.ticker` Mar 31, 2016

tacaswell added this to the 2.1 (next point release) milestone Apr 7, 2016

madphysicist added a commit to madphysicist/matplotlib that referenced this pull request Apr 8, 2016

madphysicist MAINT: Response to review comments to #6251 5161407

madphysicist ENH: Added percent formatter and tests

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madphysicist referenced this pull request Nov 17, 2016
Merged
TST: Fixed part of a test that got displaced in all the changes somehow #7467

@@ -914,6 +1009,17 @@ class EngFormatter(Formatter):
          }
          def __init__(self, unit="", places=None):
+    +        """
+    +        Initializes an engineering notation formatter.
+    +
+    +        `unit` is a string containing the abbreviated name of the unit,
+    +        suitable for use with single-letter representations of powers of
+    +        1000. For example, 'Hz' or 'm'.
+    +
+    +        `places` is the percision with which to display the number,

@@ -973,6 +1078,87 @@ def format_eng(self, num):
              return formatted.strip()
+    +class PercentFormatter(Formatter):
+    +    """
+    +    Format numbers as a percentage.
+    +
+    +    How the number is converted into a percentage is determined by the
+    +    `mx` parameter. `mx` is the data value that corresponds to 100%.
+    +    Percentages are computed as ``x / mx * 100``. So if the data is
+    +    already scaled to be percentages, `mx` will be 100. Another common
+    +    situation is where `max` is 1.0.
+    +    """
+    +    def __init__(self, mx=100, decimals=None, symbol='%'):
+    +        """
+    +        Initializes the formatter.
+    +
+    +        `max` is the data value that corresponds to 100%. `symbol` is

@@ -973,6 +1078,87 @@ def format_eng(self, num):
              return formatted.strip()
+    +class PercentFormatter(Formatter):
+    +    """
+    +    Format numbers as a percentage.
+    +
+    +    How the number is converted into a percentage is determined by the
+    +    `mx` parameter. `mx` is the data value that corresponds to 100%.
+    +    Percentages are computed as ``x / mx * 100``. So if the data is
+    +    already scaled to be percentages, `mx` will be 100. Another common
+    +    situation is where `max` is 1.0.
+    +    """
+    +    def __init__(self, mx=100, decimals=None, symbol='%'):

+    +            d = self.convert_to_pct(d) # d is a difference, so this works fine
+    +            decimals = math.ceil(2.0 - math.log10(2.0 * d))
+    +            if decimals > 5:
+    +                decimals = 5
+    +            elif decimals < 0:
+    +                decimals = 0
+    +        else:
+    +            decimals = self.decimals
+    +        s = '{x:0.{decimals}f}'.format(x=x, decimals=decimals)
+    +
+    +        if self.symbol:
+    +            return s + self.symbol
+    +        return s
+    +
+    +    def convert_to_pct(self, x):
+    +        return x / self.max * 100.0

@@ -1016,7 +1016,7 @@ def __init__(self, unit="", places=None):
              suitable for use with single-letter representations of powers of
 . For example, 'Hz' or 'm'.
-    -        `places` is the percision with which to display the number,
+    +        `places` is the prrcision with which to display the number,

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ENH: Added a `PercentFormatter` class to `matplotlib.ticker` #6251

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madphysicist commented Mar 30, 2016

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madphysicist changed the title from Added a PercentFormatter class to `matplotlib.ticker` to ENH: Added a PercentFormatter class to `matplotlib.ticker` Mar 31, 2016

madphysicist changed the title from ENH: Added a PercentFormatter class to `matplotlib.ticker` to ENH: Added a `PercentFormatter` class to `matplotlib.ticker` Mar 31, 2016

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madphysicist commented Apr 7, 2016

tacaswell added this to the 2.1 (next point release) milestone Apr 7, 2016

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efiring merged commit `c03262a` into matplotlib:master Apr 8, 2016
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