使用Dash开发交互式数据可视化网页--页面布局

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Dash应用布局

后续的操作前,需要安装如下Python包

pip install dash==0.20.0  # The core dash backend
pip install dash-renderer==0.11.2  # The dash front-end
pip install dash-html-components==0.8.0  # HTML components
pip install dash-core-components==0.18.1  # Supercharged components
pip install plotly --upgrade  # Plotly graphing library used in examples

使用Dash生成HTML

Dash应用包括两个部分，应用布局(layout)和数据交互(interactivity)。其中布局部分用来展示数据以及引导使用者使用。Dash提供了dash_core_components和dash_html_components, 以类的方式对HTML和JS进行封装，便于调用。下面先构建一个最简单的布局

import dash
import dash_core_components as dcc
import dash_html_components as htmlapp = dash.Dash()app.layout = html.Div(children=[html.H1(children = 'Hello Dash'),html.Div(children = '''Dash: A web application frameworkd for Python.'''),dcc.Graph(id = 'example-graph',figure = {'dash':[{'x': [1,2,3], 'y':[4,1,2], 'type':'bar', 'name':'SF'},{'x': [1,2,3], 'y':[2,4,5], 'type':'bar', 'name':'Montrel'},],'layout':{'title':'Dash data Visualization'}})
])if __name__ == '__main__':app.run_server(debug=True, host='0.0.0.0')

首先用app=dash.Dash()创建了Dash应用的实例，这个实例可以通过app.run_server()运行。

其次这个应用的布局(layout)由html组件(html.Div等)和图形组件(dcc.Graph等)构成。其中基础的html标签来自于dash_html_components，而更加React.js库里的高级组件则是由dash_core_components提供。

最后的展示形式需要后期慢慢的调整，比如说调整一下字体对齐, 字体颜色和背景颜色等

import dash_core_components as dcc
import dash_html_components as htmlapp = dash.Dash()colors = {'background':'#111111','text':'#7FDBFF'
}app.layout = html.Div(style={'backgroundColor':colors['background']},children=[html.H1(children = 'Hello Dash',style = {'textAlign':'center','color': colors['text']}),html.Div(children = '''Dash: A web application frameworkd for Python.''', style = {'textAlign':'center','color': colors['text']}),dcc.Graph(id = 'example-graph',figure = {'data':[{'x': [1,2,3], 'y':[4,1,2], 'type':'bar', 'name':'SF'},{'x': [1,2,3], 'y':[2,4,5], 'type':'bar', 'name':'Montreal'},],'layout':{'plot_bgcolor': colors['background'],'paper_bgcolor': colors['background'],'font':{'color': colors['text']},'title':'Dash data Visualization'}})
])if __name__ == '__main__':app.run_server(debug=True, host='0.0.0.0')

这里的html组件都设置了style，用来调整样式，

可视化

dash_core_components库中有一个Graph组件，它利用开源的JavaScript图形库--plotly.js进行交互式数据渲染。Graph里的figure参数等价于plotly.py里的figure参数，即任何plotly.js支持的图形都可以用dash_core_components调用。查看https://plot.ly/python/了解更多plotly.py的图形。

比如说这里可以基于Pandas的数据库创建散点图

import dash
import dash_core_components as dcc
import dash_html_components as html
import plotly.graph_objs as go
import pandas as pdapp = dash.Dash()df = pd.read_csv('https://gist.githubusercontent.com/chriddyp/' +'5d1ea79569ed194d432e56108a04d188/raw/' +'a9f9e8076b837d541398e999dcbac2b2826a81f8/'+'gdp-life-exp-2007.csv')plot = [dcc.Graph(id = 'life-exp-vs-GDP',figure = {'data':[go.Scatter(x=df[df['continent'] == i]['gdp per capita'],y=df[df['continent'] == i]['life expectancy'],text=df[df['continent'] == i]['country'],mode='markers',opacity=0.7,marker={'size':15,'line':{'width':0.5, 'color':'white'}},name = i) for i in df.continent.unique()],'layout': go.Layout(xaxis={'type':'log','title':'GDP per Capita'},yaxis={'title':'Life Expectancy'},margin={'l':40,'b':40,'t':10,'r':10},legend={'x':0, 'y':1},hovermode='closest')})]app.layout = html.Div(html.Div(children=[html.Div(className='col-md-4'),html.Div(plot,className='col-md-4')],className='row')
)# Append an externally hosted CSS stylesheet
my_css_url = "https://cdn.bootcss.com/bootstrap/3.3.7/css/bootstrap.min.css"
app.css.append_css({"external_url": my_css_url
})# Append an externally hosted JS bundle
my_js_url = 'https://cdn.bootcss.com/bootstrap/3.3.7/js/bootstrap.min.js'
app.scripts.append_script({"external_url": my_js_url
})if __name__ == '__main__':app.run_server(debug=True)

这部分代码将图形部分的代码从html组件中抽离出来，写完之后，再添加到html总体组件中。此外还增加了bootstrap的css样式。

Markdown语法

Dash的dash_html_components支持原生的HTML语句，而dash_core_components得Markdown提供了Markdown得渲染。

import dash
import dash_core_components as dcc
import dash_html_components as htmlapp = dash.Dash()markdown_text = '''
### Dash and MarkdownDash apps can be written in Markdown.
Dash uses the [CommonMark](http://commonmark.org/)
specification of Markdown.
Check out their [60 Second Markdown Tutorial](http://commonmark.org/help/)
if this is your first introduction to Markdown!
'''app.layout = html.Div([dcc.Markdown(children=markdown_text)
])if __name__ == '__main__':app.run_server(debug=True)

dash_core_components里不仅仅提供了Markdown, graphs这些图形组件，还支持下拉栏等其他使用工具，可在https://plot.ly/dash/dash-core-components进一步了解