Build a Shiny application

Whirlwind Zero to Application

Full tutorial from my Shiny for Python SciPy tutorial:

Plan out your application data

Start off with the data you have an some kind of data artifact without the interactivity
Use a placeholder variable to apply the interactivity manually

Visualizing penguin data

#| output-location: slide

from palmerpenguins import load_penguins
from plotnine import aes, geom_histogram, ggplot, theme_minimal

dat = load_penguins()
dat.head()

species = "Adelie"  # selected species
sel = dat.loc[dat.species == species] # selected data

(
    ggplot(aes(x="bill_length_mm"))
    + geom_histogram(dat, fill="#C2C2C4", binwidth=1)
    + geom_histogram(sel, fill="#447099", binwidth=1)
    + theme_minimal()
)

Change the species

#| output-location: slide

from palmerpenguins import load_penguins
from plotnine import aes, geom_histogram, ggplot, theme_minimal

dat = load_penguins()
dat.head()

species = "Gentoo"  # change species
sel = dat.loc[dat.species == species]

(
    ggplot(aes(x="bill_length_mm"))
    + geom_histogram(dat, fill="#C2C2C4", binwidth=1)
    + geom_histogram(sel, fill="#447099", binwidth=1)
    + theme_minimal()
)

Radio Buttons

#| '!! shinylive warning !!': |
#|   shinylive does not work in self-contained HTML documents.
#|   Please set `embed-resources: false` in your metadata.
# | standalone: true
# | components: [editor, viewer]
# | layout: horizontal
from shiny.express import ui

ui.input_radio_buttons(
    id="species",
    label="Species",
    choices=["Adelie", "Gentoo", "Chinstrap"],
)

Run your application

Positron/VS Code + Shiny Extension

Command line:

shiny run --reload app.py

Radio Buttons: options

https://shiny.posit.co/py/api/express/express.ui.input_radio_buttons.html

#| '!! shinylive warning !!': |
#|   shinylive does not work in self-contained HTML documents.
#|   Please set `embed-resources: false` in your metadata.
# | standalone: true
# | components: [editor, viewer]
# | layout: horizontal
from shiny.express import ui

ui.input_radio_buttons(
    id="species",
    label="Species",
    choices=["Adelie", "Gentoo", "Chinstrap"],
    inline=True,
)

Add in the figure

Now let’s add all that data and plotting code from earlier into our application.

If we just dump in our code, the application errors because it does not know what to do with the figure that’s trying to be printed.

Output will error

#| '!! shinylive warning !!': |
#|   shinylive does not work in self-contained HTML documents.
#|   Please set `embed-resources: false` in your metadata.
# | standalone: true
# | components: [editor, viewer]
# | layout: horizontal
from shiny.express import ui

from palmerpenguins import load_penguins
from plotnine import aes, geom_histogram, ggplot, theme_minimal

ui.input_radio_buttons(
    id="species",
    label="Species",
    choices=["Adelie", "Gentoo", "Chinstrap"],
    inline=True,
)

dat = load_penguins()
species = "Adelie"
sel = dat.loc[dat.species == species]

# this will cause a TypeError: Invalid tag item type
(
    ggplot(aes(x="bill_length_mm"))
    + geom_histogram(dat, fill="#C2C2C4", binwidth=1)
    + geom_histogram(sel, fill="#447099", binwidth=1)
    + theme_minimal()
)

Outputs

Each output needs to be wrapped in it’s own function with the corresponding output decorator.

https://shiny.posit.co/py/components/#outputs

We now need to use one of the built-in Shiny output components,
Specifically, one that can render a plotnine figure (which is based on matplotlib), plot output component.
For example, we want to return a plot, so we will need to wrap our plotnine code, and decorate it with the @render.plot decorator.

Render plot output

@render.plot #<<
def plot(): #<<
    return ( #<<
        ggplot(aes(x="bill_length_mm"))
        + geom_histogram(dat, fill="#C2C2C4", binwidth=1)
        + geom_histogram(sel, fill="#447099", binwidth=1)
        + theme_minimal()
    )

Return the output

Don’t forget to return the object you want displayed in the function! Otherwise the output will not render.

Render plot output

#| '!! shinylive warning !!': |
#|   shinylive does not work in self-contained HTML documents.
#|   Please set `embed-resources: false` in your metadata.
# | standalone: true
# | components: [editor, viewer]
# | layout: horizontal
from shiny.express import ui, render

from palmerpenguins import load_penguins
from plotnine import aes, geom_histogram, ggplot, theme_minimal

ui.input_radio_buttons(
    id="species",
    label="Species",
    choices=["Adelie", "Gentoo", "Chinstrap"],
    inline=True,
)

dat = load_penguins()
species = "Adelie"
sel = dat.loc[dat.species == species]

@render.plot #<<
def plot(): #<<
    return ( #<<
        ggplot(aes(x="bill_length_mm"))
        + geom_histogram(dat, fill="#C2C2C4", binwidth=1)
        + geom_histogram(sel, fill="#447099", binwidth=1)
        + theme_minimal()
    )

Reactivity

But the radio buttons don’t change anything
We didn’t connect the input component to the output component
Reactivity is what makes Shiny unique

The data reacts to the input

dat = load_penguins()

@render.plot
def plot():
    species = input.species() #<<
    sel = dat.loc[dat.species == species] #<<

    return (
        ggplot(aes(x="bill_length_mm"))
        + geom_histogram(dat, fill="#C2C2C4", binwidth=1)
        + geom_histogram(sel, fill="#447099", binwidth=1)
        + theme_minimal()
    )

Your first application

#| '!! shinylive warning !!': |
#|   shinylive does not work in self-contained HTML documents.
#|   Please set `embed-resources: false` in your metadata.
#| standalone: true
#| components: [editor, viewer]
#| layout: horizontal
#| viewerHeight: 500

from palmerpenguins import load_penguins
from plotnine import aes, geom_histogram, ggplot, theme_minimal
from shiny.express import input, render, ui

dat = load_penguins().dropna()
species = dat["species"].unique().tolist()

ui.input_radio_buttons("species", "Species", species, inline=True)


@render.plot
def plot():
    sel = dat[dat["species"] == input.species()]
    return (
        ggplot(aes(x="bill_length_mm"))
        + geom_histogram(dat, fill="#C2C2C4", binwidth=1)
        + geom_histogram(sel, fill="#447099", binwidth=1)
        + theme_minimal()
    )

05:00