holoviews

name	holoviews
description	Build interactive visualizations with HoloViews elements, opts, streams, and operations. Use when composing plots from element primitives (Curve, Points, Bars, NdOverlay), customizing Bokeh tools/tooltips/formatters, using DynamicMap, streams, or link_selections. Do not use for simple DataFrame plotting (use hvPlot) or Panel app structure (use Panel).
metadata	{"version":"0.0.3","author":"holoviz"}

Using HoloViews

HoloViews lets you build interactive visualizations by composing declarative elements. Use it when you need fine-grained control over plot composition, custom tooltips, Bokeh tool configuration, streaming data, or cross-filtering — things that go beyond hvPlot's .plot()-style API.

For embedding HoloViews plots in Panel apps (DynamicMap trigger pattern, responsive sizing, pn.pane.HoloViews), see Plotting in Panel.

Contents

• Opts System
• Hover Tooltips
• Formatters
• Bokeh Tools
• DynamicMap
• Streams

Opts System

.opts() applies visual options to elements. Chain calls for different element types.

# Options on the element itself
hv.Curve(df, "date", "revenue").opts(
    color="blue", line_width=2, responsive=True, height=300,
)

# Chained opts for container + element type
hv.NdOverlay(curves, kdims=["Region"]).opts(
    "NdOverlay", legend_position="top_left", title="Revenue by Region",
).opts(
    "Curve", responsive=True, height=350, tools=["hover"],
)

• Options go on the element type they belong to: legend_position and title on NdOverlay, tools and color on Curve.
• Misplaced options raise ValueError: unexpected option 'X' for Y type.
• A legend with a single entry distinguishes nothing and just adds clutter — suppress it: .opts(show_legend=len(groups) > 1) (computed from the same dict/groupby driving the NdOverlay, e.g. after a filter narrows a by=/kdims= grouping down to one category).
• .opts() on pure HoloViews elements is fine. For hvPlot, pass options as hvplot kwargs instead — see the hvPlot skill.

Hover Tooltips

Use hover_tooltips as an opts list of (label, value) tuples. Bokeh format strings apply inside {}.

hv.Curve(df, "date", "revenue").opts(
    tools=["hover"],
    hover_tooltips=[
        ("Date", "@{date}"),
        ("Revenue", "@revenue{$0,0}"),
        ("Region", "$name"),           # $name = NdOverlay key
    ],
)

• @column or @{column} references data columns. Use @{col name} for names with spaces.
• $name references the NdOverlay key (legend label).
• Bokeh format syntax: {$0,0} currency with thousands, {0.1f} one decimal, {0,0} thousands, {%F %H:%M} datetime.
• hover_formatters is deprecated — do not use it. Format inline in the tooltip string.
• hover_mode="vline" snaps tooltip to nearest x-value — ideal for timeseries and cumulative curves.

Formatters

Import from bokeh.models for axis formatting:

from bokeh.models import NumeralTickFormatter, DatetimeTickFormatter

hv.Curve(df, "date", "revenue").opts(
    yformatter=NumeralTickFormatter(format="$0,0"),
    xformatter=DatetimeTickFormatter(months="%b %Y"),
)

Common NumeralTickFormatter formats: "$0,0" (currency), "0,0" (thousands), "0a" (abbreviated: 1k, 1M), "0.0%" (percentage).

Bokeh Tools

Control the toolbar via tools, default_tools, and active_tools:

hv.Curve(df, "date", "revenue").opts(
    tools=["hover", "xwheel_zoom"],       # add these tools
    active_tools=["xwheel_zoom"],          # active by default
    default_tools=["reset"],               # keep only reset from defaults
)

• default_tools=[] strips all default Bokeh tools (pan, wheel_zoom, save, reset). Add back selectively: default_tools=["reset"].
• tools= adds on top of defaults. Common: "hover", "xwheel_zoom", "ywheel_zoom", "box_select", "tap", "lasso_select".
• active_tools= sets which tools are active on load.

DynamicMap

DynamicMap calls a callback to generate elements lazily. It patches data in place, preserving zoom/pan — unlike replacing pane.object which resets axes.

dmap = hv.DynamicMap(render_fn, streams=[stream])

• Each DynamicMap callback must always return the same element type. Returning Scatter sometimes and NdOverlay other times raises AssertionError.
• Create one DynamicMap per element type, combine with * (overlay) or + (layout).
• Use .opts(framewise=True) with streaming data (Pipe/Buffer) so axes update when data ranges change.

For the Panel integration pattern (trigger param, pn.bind, pn.pane.HoloViews), see Plotting in Panel.

Streams

Streams push events from user interactions or external data into DynamicMap callbacks. The basic pattern: create a stream with source=element, write a callback that receives stream values, wrap in hv.DynamicMap(callback, streams=[stream]).

Common streams: Selection1D (indices from tap/box_select), Tap (x/y coordinates), PointerX/PointerY (cursor position), BoundsX/BoundsXY (selection range), Pipe (replace data), Buffer (append data). Use .opts(framewise=True) with Pipe/Buffer so axes update when data ranges change.

PointerX / PointerY (Linked Cross-Sections)

Track cursor position on one plot to update a linked detail view — useful for Hovmueller cross-sections, distributions at a cursor position, etc.

geomap = hv.Image(ds.isel(time=0), ["lon", "lat"], ["air"]).opts(tools=["hover"])
lat_stream = hv.streams.PointerY(y=40, source=geomap)

def create_xsection(y):
    return hv.Image(ds.sel(lat=y, method="nearest"), ["lon", "time"], ["air"])

def create_hline(y):
    return hv.HLine(y).opts(color="red")

# One DynamicMap per element type, combine with *
layout = geomap * hv.DynamicMap(create_hline, streams=[lat_stream]) \
       + hv.DynamicMap(create_xsection, streams=[lat_stream])

BoundsX (Subset Axis Limits)

Use xbox_select and .apply.opts(xlim=stream.param.boundsx) to drive axis range — no callback needed.

source = hv.Curve(df, "x", "y").opts(
    width=500, height=125, default_tools=["xbox_select"],
)
stream = hv.streams.BoundsX(source=source, boundsx=(0, 2))

target = (hv.Curve(df, "x", "y") * hv.Scatter(df, "x", "y")).opts(
    "Curve", axiswise=True, framewise=True, width=500, height=250,
)
target = target.apply.opts(xlim=stream.param.boundsx)

layout = (source + target).opts(merge_tools=False).cols(1)

Pitfalls

• Selection1D needs tools=['tap', 'box_select'] in .opts() — without them no events fire.
• Stream callbacks receive None/empty on first render — always guard with if x is None.
• Always set source= on the stream. For bidirectional interaction, create separate streams with separate sources.
• Don't mix streams and param.depends/pn.bind for the same plot.

Cross-Filtering with link_selections

hv.link_selections provides automatic cross-filtering across static elements.

• Does NOT work with DynamicMap — use Tabulator selection + pn.bind(watch=True) instead (see examples/dashboard.py in the Panel skill).
• Use .instance() to create a reusable linker.
• hv.operation.histogram(element, dimension='x') for numeric histograms — preserves data lineage.
• For categorical bars, subclass hv.Operation (see below).
• Don't add selection tools manually — link_selections adds them.
• Requires pyarrow at runtime. Lasso also requires shapely.

from holoviews.operation import histogram

ls = hv.link_selections.instance()
scatter = hv.Points(df, kdims=["x", "y"])
hist = histogram(scatter, dimension="x", num_bins=20)
layout = ls(scatter) + ls(hist)

Categorical Bars with link_selections

import numpy as np

class categorical_agg(hv.Operation):
    dimension = param.String(doc="Categorical dimension to group by")
    value_dimension = param.String(default=None, allow_None=True)
    function = param.Callable(default=np.size)
    label = param.String(default=None, allow_None=True)

    def _process(self, element, key=None):
        cat_vals = element.dimension_values(self.p.dimension, expanded=True)
        unique_cats = np.unique(cat_vals)
        if self.p.value_dimension is None:
            _, counts = np.unique(cat_vals, return_counts=True)
            data = list(zip(unique_cats, counts))
            agg_label = self.p.label or "Count"
        else:
            num_vals = element.dimension_values(self.p.value_dimension, expanded=True)
            results = [self.p.function(num_vals[cat_vals == cat]) for cat in unique_cats]
            agg_label = self.p.label or f"{self.p.value_dimension}"
            data = list(zip(unique_cats, results))
        return hv.Bars(data, kdims=[self.p.dimension], vdims=[agg_label])

bars = categorical_agg(scatter, dimension="species")
layout = ls(scatter) + ls(bars)

Lookup

Search the web at https://holoviews.org/search.html?q=<topic> for additional information.