plotly-express figure color legend should display only integer values

Question

A graph created with plotly express using a choropleth map shows distribution of count values associated to the regions of Italy:

import pandas as pd
import requests
import plotly.express as px

data = {'regions' : ['Piemonte', 'Trentino-Alto Adige', 'Lombardia', 'Puglia', 'Basilicata', 
           'Friuli Venezia Giulia', 'Liguria', "Valle d'Aosta", 'Emilia-Romagna',
           'Molise', 'Lazio', 'Veneto', 'Sardegna', 'Sicilia', 'Abruzzo',
           'Calabria', 'Toscana', 'Umbria', 'Campania', 'Marche'],
        'counts' : [3, 3, 4, 2, 0,
                    4, 4, 0, 0,
                    1, 1, 0, 3, 4, 4,
                    3, 4, 3, 2, 4]}

df = pd.DataFrame.from_dict(data)

# Read the geojson data with Italy's regional borders [enter image description here][2]from github
repo_url = 'https://gist.githubusercontent.com/datajournalism-it/48e29e7c87dca7eb1d29/raw/2636aeef92ba0770a073424853f37690064eb0ea/regioni.geojson'
italy_regions_geo = requests.get(repo_url).json()

fig = px.choropleth(data_frame=df, 
                    geojson=italy_regions_geo, 
                    locations='regions', # name of dataframe column matching the region names
                    featureidkey='properties.NOME_REG',  # path to field in GeoJSON feature object with which to match the values passed in to locations
                    color='counts',
                    color_continuous_scale="Magma",
                    scope="europe",
                   )
fig.update_geos(resolution=50, 
                showcountries=False, 
                showcoastlines=False, 
                fitbounds="locations",
                showland=False)

fig.update_layout(margin={"r":0,"t":0,"l":0,"b":0})
fig.show()
fig.write_image("./italy.png") 

when the maximum value of count is four, the figure color legend will include labels with decimals, which is not needed, given that values should be treated as integers. Decimals disappear as soon as the maximum value of count is 5, or larger. How do I control the appearance of decimals in the figure color legend?

Answer 1

• it's documented here https://plotly.com/python/reference/layout/coloraxis/#layout-coloraxis-colorbar-dtick
• hence one additional layout instruction below

import pandas as pd
import requests
import plotly.express as px

data = {'regions' : ['Piemonte', 'Trentino-Alto Adige', 'Lombardia', 'Puglia', 'Basilicata', 
           'Friuli Venezia Giulia', 'Liguria', "Valle d'Aosta", 'Emilia-Romagna',
           'Molise', 'Lazio', 'Veneto', 'Sardegna', 'Sicilia', 'Abruzzo',
           'Calabria', 'Toscana', 'Umbria', 'Campania', 'Marche'],
        'counts' : [3, 3, 4, 2, 0,
                    4, 4, 0, 0,
                    1, 1, 0, 3, 4, 4,
                    3, 4, 3, 2, 4]}

df = pd.DataFrame.from_dict(data)

# Read the geojson data with Italy's regional borders [enter image description here][2]from github
repo_url = 'https://gist.githubusercontent.com/datajournalism-it/48e29e7c87dca7eb1d29/raw/2636aeef92ba0770a073424853f37690064eb0ea/regioni.geojson'
italy_regions_geo = requests.get(repo_url).json()

fig = px.choropleth(data_frame=df, 
                    geojson=italy_regions_geo, 
                    locations='regions', # name of dataframe column matching the region names
                    featureidkey='properties.NOME_REG',  # path to field in GeoJSON feature object with which to match the values passed in to locations
                    color='counts',
                    color_continuous_scale="Magma",
                    scope="europe",
                   )
fig.update_geos(resolution=50, 
                showcountries=False, 
                showcoastlines=False, 
                fitbounds="locations",
                showland=False)

fig.update_layout(margin={"r":0,"t":0,"l":0,"b":0})
fig.update_layout(coloraxis={"colorbar":{"dtick":1}})
fig.show()