Repeating same tick values

[ostrolucky]

See Y axis? This is caused because we are returning rounded value in options.yAxes.ticks.callback. So chart.js calls callback with 0, 0.1 ... 0.9, 1.0, 1.1 values, but callback returns 0, 1 only. Repeating same values in a chart is undesirable for end user.

In userspace, I've applied following fix to solve this issue:

// this is to prevent repeating tick values
var middlewareToMakeTicksUnique = function(next) {
    return function(value, index, values) {
        var nextValue = next(value);

        if (index && values.length > index+1 && // always show first and last tick
            // don't show if next or previous tick is same
            (next(values[index + 1]) === nextValue || next(values[index - 1]) === nextValue)
        ) {
            return null;
        }

        return nextValue;
    }
};

...

yAxes: [{
    ticks: {
        callback: middlewareToMakeTicksUnique(function (value) {
            return value.format();
        })
    }
}]

[etimberg]

@ostrolucky do you have a fiddle that reproduces this?

[ostrolucky]

https://jsfiddle.net/mgt1ybx0/

[etimberg]

I'm not entirely convinced this is a bug. The callback is explicitly formatting the string values for ticks like 0.8 to be 1 and so 1 is displayed. The conversion to strings happens after all the ticks have been calculated.

Using a callback to only display certain ticks is recommended. Here I've written a simple one that only returns ticks that are integers and removes the others. If you want grid lines to show up for the hidden ticks, return '' instead of null.

[ostrolucky]

I don't care about classification of this, I never mentioned it's a bug. I don't see current behaviour as sensible though. I don't see any use case where it's useful when values shown there are duplicated, do you? I also don't see why is developer forced to work around this. Developer never provided non-integer value, but Chart.js tries to display them. I've never see this in other charting solutions.

[ostrolucky]

Closing as this is unlikely to be fixed.

[sstruct]

@etimberg same here. I need to format ticks' value with different units, this solution couldn't help.

Can this issue be reopened please?

[sstruct]

Worked out a temporary solution:

ticks: {
  beginAtZero: true,
  // formatValue convert value to be suffixed, eg: 0.2 -> 20%
  callback: value => formatValue(value),
  /**
   * userCallback
   * @param label
   * @param index
   * @param labels
   * @return {*}
   */
  userCallback: (label, index, labels) => {
    // _ refers to [lodash](https://lodash.com/)
    if ((_.every(labels, lb => Math.abs(lb) < 1) && Math.floor(label * 100) === label.toFixed(4) * 100)
          || Math.floor(label) === label
          || index === 0) {
      return formatValue(label);
    }
  },
},

ref: https://stackoverflow.com/questions/37699485/skip-decimal-points-on-y-axis-in-chartjs

---

Another Solution Now:

/**
 * fix issue: https://trello.com/c/7MeGZsmu
 * @param label
 * @param index
 * @param labels
 * @return {*}
 */
userCallback: function(label, index, labels) {
  const formatedLabel = formatValue(label, unitDesc);
  const formatedLabels = _.map(labels, lb => formatValue(lb, unitDesc));
  const counts = _.countBy(formatedLabels);
  if (counts[formatedLabel] === 1
    || index === labels.length - 1
    || index === 0) {
    return formatedLabel;
  }
},

[ostrolucky]

Since I see other people have same problem, reopening

[sabelofficial]

It'd be great if this would be fixed soon

[etimberg]

There is a proposal to add a way of forcing integer steps in #4841

[nagix]

Closing as this was solved in #4841 and is already available in version 2.7.3 (setting ticks.precision to 0, no need for callback).

[pimvanderheijden]

Using precision: 0 (or even { precision: 0, integerSteps: true }) and still have repeating tick values, as described above

version 2.7.3

[pimvanderheijden]

I got it working now. What helped was converting the (y) values first, before constructing a label in ticks.callback . Appears to me that Chart.js does filter identical values only before the callback and not after.

[eakkew]

I got the solution by using suggestedMin, suggestedMax, and stepSize

https://www.chartjs.org/docs/latest/axes/cartesian/linear.html#axis-range-settings

[JIGARKAPADIYA]

Repeating values are not seen in graph any one who has resolved it please send the 'options' of chart

[tapistefan]

I was struggling with this problem for hours at last "precision: 0" solved this for me.
options: { scales: { yAxes: [{ ticks: { beginAtZero: false, fontSize: 20, precision:0 } }] } }

[tansinjahan]

I got it working now. What helped was converting the (y) values first, before constructing a label in ticks.callback . Appears to me that Chart.js does filter identical values only before the callback and not after.

@pimvanderheijden I am facing the same problem and my current code converts the y-value inside callback function and then constructs the label inside. Could you please give more context about how did you manage to filter the identical values before the callback??

[pimvanderheijden]

I think I meant I mapped the set of x and y values [{ t, y }, ... ] first so that the x has the right format before going into Chart.js.

const original = [{ t1, y2 }, { t2, y2 } ]
const chartJsReady = original.map(({ t, y }) => { return { t: new Date(t).toISOString(), y })

Not really sure if this answer the question honestly

[tansinjahan]

I think I meant I mapped the set of x and y values [{ t, y }, ... ] first so that the x has the right format before going into Chart.js.

const original = [{ t1, y2 }, { t2, y2 } ]
const chartJsReady = original.map(({ t, y }) => { return { t: new Date(t).toISOString(), y })

Not really sure if this answer the question honestly
Doesn't solve my problem 100% so had to do some workaround but yeah thanks for replying.