Title: HeatMap Tap stream example
Description: A linked streams example demonstrating how use Tap stream on a HeatMap. The data contains the incidence of measles across US states by year and week (obtained from [Project Tycho](http://www.tycho.pitt.edu/)). The HeatMap represents the mean measles incidence per year. On tap the Histogram on the right will generate a Histogram of the incidences for each week in the selected year and state.
Backends: Bokeh
Tags: streams, tap, interactive



In [ ]:

    
import pandas as pd
import numpy as np
import holoviews as hv
from holoviews import opts

hv.extension('bokeh', width=90)



In [ ]:

    
# Declare dataset
df = pd.read_csv('http://assets.holoviews.org/data/diseases.csv.gz', compression='gzip')
dataset = hv.Dataset(df, vdims=('measles','Measles Incidence'))

# Declare HeatMap
heatmap = hv.HeatMap(dataset.aggregate(['Year', 'State'], np.mean),
                     label='Measles Incidence').select(Year=(1928, 2002))

# Declare Tap stream with heatmap as source and initial values
posxy = hv.streams.Tap(source=heatmap, x=1951, y='New York')

# Define function to compute histogram based on tap location
def tap_histogram(x, y):
    return hv.Curve(dataset.select(State=y, Year=int(x)), kdims='Week',
                   label='Year: %s, State: %s' % (x, y))

tap_dmap = hv.DynamicMap(tap_histogram, streams=[posxy])

(heatmap + tap_dmap).opts(
    opts.Curve(framewise=True, height=500, line_color='black', width=375, yaxis='right'),
    opts.HeatMap(cmap='RdBu_r', fontsize={'xticks': '6pt'}, height=500,
                 logz=True, tools=['hover'], width=700, xrotation=90)
)