class_docstr: A histogram of a categorial field.
  
  Args:
      field_or_expr: a field name, ``embedded.field.name``,
          :class:`fiftyone.core.expressions.ViewExpression`, or
          `MongoDB expression <https://docs.mongodb.com/manual/meta/aggregation-quick-reference/#aggregation-expressions>`_
          defining the field or expression to plot
      expr (None): an optional
          :class:`fiftyone.core.expressions.ViewExpression` or
          `MongoDB expression <https://docs.mongodb.com/manual/meta/aggregation-quick-reference/#aggregation-expressions>`_
          to apply to ``field_or_expr`` (which must be a field) before
          plotting
      order ("alphabetical"): the x-axis ordering strategy to use. Can be
          "alphabetical" to sort by field value, or "frequency" to sort in
          descending order of frequency, or a function suitable for
          ``sorted(items, key=order)``, where ``items`` is a list of
          ``(value, count)`` tuples
      xlabel (None): an optional x-label for the plot
      log (False): whether to use a log scale y-axis
      bargap (None): relative spacing between bars in ``[0, 1]``
      color (None): a color for the bars. Can be any color supported by
          :meth:`plotly:plotly.graph_objects.bar.Marker.color`
      opacity (None): an optional opacity for the bars in ``[0, 1]``
      init_view (None): an optional initial
          :class:`fiftyone.core.collections.SampleCollection` to load
      **kwargs: optional parameters for
          :meth:`plotly:plotly.graph_objects.Figure.update_layout`
code: def _make_histogram(self):
      if etau.is_str(self.field_or_expr):
          _field = self.field_or_expr.rsplit(".", 1)[-1]
      else:
          _field = "value"
  
      hover_lines = [
          "<b>%s: %%{x}</b>" % _field,
          "count: %{y}",
      ]
      hovertemplate = "<br>".join(hover_lines) + "<extra></extra>"
  
      if self.color is None:
          marker_color = _DEFAULT_MARKER_COLOR
      else:
          marker_color = self.color
  
      bar = go.Bar(
          hovertemplate=hovertemplate,
          marker_color=marker_color,
          opacity=self.opacity,
      )
  
      if self.xlabel is not None:
          xaxis_title = self.xlabel
      elif etau.is_str(self.field_or_expr):
          xaxis_title = self.field_or_expr
      else:
          xaxis_title = None
  
      layout = _DEFAULT_LAYOUT.copy()
  
      layout.update(
          dict(
              xaxis_title=xaxis_title,
              yaxis_title="count",
              bargap=self.bargap,
          )
      )
  
      if self.log:
          layout.update(dict(yaxis_type="log"))
  
      layout.update(self.layout)
  
      figure = go.Figure(bar)
      figure.update_layout(**layout)
  
      return figure
  
imports: import itertools
  from operator import itemgetter
  import numpy
  import eta.core.utils
  import plotly.subplots
  import plotly.graph_objects
  import fiftyone.core.aggregations
  from .base import ViewPlot
  from .plotly import PlotlyWidgetMixin
label_desc: Use image node_id 3 for calling the CategoricalHistogram obj's underlying member method code with example usage: obj._make_histogram() and returns: figure