Plotly.express、熊猫和 NaN

Posted 2023-02-18

【中文标题】Plotly.express、熊猫和 NaN

【英文标题】：Plotly.express, pandas and NaNs

【发布时间】：2021-12-15 19:26:21

【问题描述】：

根据下面的代码，我想以绘图方式可视化我的数据。但是，我创建的饼图也显示了 Null，我想省略它。

import dash
import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output
import plotly.express as px
import pandas as pd

df = pd.DataFrame([
        ['January', 'Violin'],
        ['February', 'Piano'], 
        ['March', 'Violin'],
        ['February', 'Violin'],
        ['January', 'Piano'],
        ['January', 'Violin']], 
    columns=['Month', 'Instrument']
)

df = df.pivot(columns='Month', values='Instrument')

app = dash.Dash(__name__)

app.layout = html.Div([
    html.P("Select a month:"),
    dcc.Dropdown(
        id='my_dropdown',
        value = 'January',
        options=[
                  'label': 'January', 'value': 'January',
                  'label': 'February', 'value': 'February',
                  'label': 'March', 'value': 'March'
        ],
        clearable=False,
        style="width": "50%"
    ),
    dcc.Graph(id="pie-chart"),
])

@app.callback(
    Output("pie-chart", "figure"),
    [Input("my_dropdown", "value")])
def generate_chart(my_dropdown):
    fig = px.pie(df, names=my_dropdown)
    return fig

app.run_server(debug=True)

在这种情况下，我应该将某些内容更改为代码的情节部分，还是应该以不同的方式转换我的初始 DataFrame（而不是使用 df.pivot() 选项）？

【参考方案1】：

看起来你想要的是每个仪器实例数的计数，所以我认为你不需要旋转你的 DataFrame。你可以保持原样：

df
      Month Instrument
0   January     Violin
1  February      Piano
2     March     Violin
3  February     Violin
4   January      Piano
5   January     Violin

如果您将参数names='Instrument' 传递给px.pie，它将通过计算Instrument 列中唯一值的出现次数来创建饼图，您不必担心出现空值。然后，您可以按用户在 generate_chart 函数中以破折号选择的月份对 DataFrame 进行子集化。

import dash
import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output
import plotly.express as px
import pandas as pd

df = pd.DataFrame([
        ['January', 'Violin'],
        ['February', 'Piano'], 
        ['March', 'Violin'],
        ['February', 'Violin'],
        ['January', 'Piano'],
        ['January', 'Violin']], 
    columns=['Month', 'Instrument']
)

# df = df.pivot(columns='Month', values='Instrument')

app = dash.Dash(__name__)

app.layout = html.Div([
    html.P("Select a month:"),
    dcc.Dropdown(
        id='my_dropdown',
        value = 'January',
        options=[
                  'label': 'January', 'value': 'January',
                  'label': 'February', 'value': 'February',
                  'label': 'March', 'value': 'March'
        ],
        clearable=False,
        style="width": "50%"
    ),
    dcc.Graph(id="pie-chart"),
])

@app.callback(
    Output("pie-chart", "figure"),
    [Input("my_dropdown", "value")])
def generate_chart(my_dropdown):
    fig = px.pie(
        df[df['Month'] == my_dropdown], 
        names='Instrument'
    )
    # fig = px.pie(df, names=my_dropdown)
    return fig

app.run_server(debug=True)