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Fix issue #4928: linear tick generator doesn't round values to needed precision. #4943

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merged 5 commits into from Dec 2, 2017

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jcopperfield
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@jcopperfield jcopperfield commented Nov 13, 2017

Fixes #4928 - linear tick generator doesn't round values to needed precision.

Test case: https://codepen.io/anon/pen/LOLxvL

v2.7
issue_tick_rounding_error_4928
Proposed fix
fix-issue_tick_rounding_error_4928

 - linear tick generator doesn't round values to needed precision.
// Put the values into the ticks array
var precision = 1;
if (spacing < 1) {
precision = Math.pow(10, spacing.toPrecision().length - 2);
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Would it be equivalent to replace .toPrecision() with .toString()? I think that would make it clearer

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In this case I think they both return equal results. Since the code is trying to find the number of significant digits after the decimal point.

@benmccann
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You're on a roll! This is great!

@jcopperfield
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jcopperfield commented Nov 14, 2017

The logarithmic tick generator contains the same problem.
v2.7
issue_logarithmic_tick_rounding_error
PR Fix: logarithmic tick generator doesn't round values to needed precision ad984be
fix_issue_logarithmic_tick_rounding_error png

@simonbrunel simonbrunel added this to the Version 2.8 milestone Nov 14, 2017
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Rounding negative values didn't create the expected result
v.2.7
issue_rounding_negative_tick_values
PR Fix: rounding tick values didn't work for negative values. 37bfadb
fix_issue_rounding_negative_tick_values

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Could be useful to unit test these expected values (positive and negative)?

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jcopperfield commented Nov 14, 2017

Where is such a test best placed, and should the test be run directly on the generators.linear function or on a chart?

BTW a lot of test code use the function toBeCloseTo like expect(number).toBeCloseTo(10, 1e-4), however jasmine documentation describes the second parameter as precisionopt:

toBeCloseTo(expected, precisionopt)
expect the actual value to be within a specified precision of the expected value.
Parameters:

Name Type Attributes Default Description
expected Object     The expected value to compare against.
precision Number 2 The number of decimal points to check.

example
expect(number).toBeCloseTo(42.2, 3);

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I don't think tests can run directly on generators because they are not accessible from Chart.*, so it would require to generate a chart and test generated values from ticks (as all other tests). I would still keep these tests in a new core.ticks.tests.js to make easier source/test mapping (as I would do for the layout PR).

Not sure why toBeCloseTo(10, 1e-4) (@etimberg), might be a good idea to update those checks with proper values.

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Agree about testing on a real chart.

For the toBeCloseTo I must have misread the documentation when it was added. Lets fix that

@etimberg etimberg merged commit 6f34b22 into chartjs:master Dec 2, 2017
@jcopperfield jcopperfield deleted the PR-20171113-4928 branch December 3, 2017 07:37
yofreke pushed a commit to yofreke/Chart.js that referenced this pull request Dec 30, 2017
… needed precision. (chartjs#4943)

* Fix issue 4928
 - linear tick generator doesn't round values to needed precision.

* Improve: replace toPrecision() in toString() to improve readability.

* Fix: logarithmic tick generator doesn't round values to needed precision.

* Fix: rounding tick values didn't work for negative values.

* Add: Core ticks tests
exwm pushed a commit to exwm/Chart.js that referenced this pull request Apr 30, 2021
… needed precision. (chartjs#4943)

* Fix issue 4928
 - linear tick generator doesn't round values to needed precision.

* Improve: replace toPrecision() in toString() to improve readability.

* Fix: logarithmic tick generator doesn't round values to needed precision.

* Fix: rounding tick values didn't work for negative values.

* Add: Core ticks tests
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Line chart render yAxes error with number "0.6"
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