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