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Plotly Express Arguments in Python

Input data arguments accepted by Plotly Express functions


New to Plotly?

Plotly is a free and open-source graphing library for Python. We recommend you read our Getting Started guide for the latest installation or upgrade instructions, then move on to our Plotly Fundamentals tutorials or dive straight in to some Basic Charts tutorials.

Plotly Express works with Column-oriented, Matrix or Geographic Data

Plotly Express provides functions to visualize a variety of types of data. Most functions such as px.bar or px.scatter expect to operate on column-oriented data of the type you might store in a Pandas DataFrame (in either "long" or "wide" format, see below). px.imshow operates on matrix-like data you might store in a numpy or xarray array and functions like px.choropleth and px.choropleth_mapbox can operate on geographic data of the kind you might store in a GeoPandas GeoDataFrame. This page details how to provide column-oriented data to most Plotly Express functions.

Plotly Express works with Long-, Wide-, and Mixed-Form Data

Until version 4.8, Plotly Express only operated on long-form (previously called "tidy") data, but now accepts wide-form and mixed-form data as well.

There are three common conventions for storing column-oriented data, usually in a data frame with column names:

  • long-form data has one row per observation, and one column per variable. This is suitable for storing and displaying multivariate data i.e. with dimension greater than 2. This format is sometimes called "tidy".
  • wide-form data has one row per value of one of the first variable, and one column per value of the second variable. This is suitable for storing and displaying 2-dimensional data.
  • mixed-form data is a hybrid of long-form and wide-form data, with one row per value of one variable, and some columns representing values of another, and some columns representing more variables. See the wide-form documentation for examples of how to use Plotly Express to visualize this kind of data.

Every Plotly Express function other than imshow can operate on long-form data, and in addition, the following 2D-Cartesian functions can operate on wide-form and mixed-form data: px.scatter, px.line, px.area, px.bar, px.histogram, px.violin, px.box, px.strip, px.funnel, px.density_heatmap and px.density_contour.

By way of example here is the same data, represented in long-form first, and then in wide-form:

In [1]:
import plotly.express as px
long_df = px.data.medals_long()
long_df
Out[1]:
nation medal count
0 South Korea gold 24
1 China gold 10
2 Canada gold 9
3 South Korea silver 13
4 China silver 15
5 Canada silver 12
6 South Korea bronze 11
7 China bronze 8
8 Canada bronze 12
In [2]:
import plotly.express as px
wide_df = px.data.medals_wide()
wide_df
Out[2]:
nation gold silver bronze
0 South Korea 24 13 11
1 China 10 15 8
2 Canada 9 12 12

Plotly Express can produce the same plot from either form:

In [3]:
import plotly.express as px
long_df = px.data.medals_long()

fig = px.bar(long_df, x="nation", y="count", color="medal", title="Long-Form Input")
fig.show()
In [4]:
import plotly.express as px
wide_df = px.data.medals_wide()

fig = px.bar(wide_df, x="nation", y=["gold", "silver", "bronze"], title="Wide-Form Input")
fig.show()

You might notice that y-axis and legend labels are slightly different for the second plot: they are "value" and "variable", respectively, and this is also reflected in the hoverlabel text. This is because Plotly Express performed an internal Pandas melt() operation to convert the wide-form data into long-form for plotting, and used the Pandas convention for assign column names to the intermediate long-form data. Note that the labels "medal" and "count" do not appear in the wide-form data frame, so in this case, you must supply these yourself, or you can use a data frame with named row- and column-indexes. You can rename these labels with the labels argument:

In [5]:
import plotly.express as px
wide_df = px.data.medals_wide()

fig = px.bar(wide_df, x="nation", y=["gold", "silver", "bronze"], title="Wide-Form Input, relabelled",
            labels={"value": "count", "variable": "medal"})
fig.show()

Many more examples of wide-form and messy data input can be found in our detailed wide-form support documentation.

Input Data as Pandas DataFrames

As shown above, px functions supports natively pandas DataFrame. Arguments can either be passed as dataframe columns, or as column names if the data_frame argument is provided.

Passing columns as arguments

In [6]:
import plotly.express as px
df = px.data.iris()
# Use directly Columns as argument. You can use tab completion for this!
fig = px.scatter(df, x=df.sepal_length, y=df.sepal_width, color=df.species, size=df.petal_length)
fig.show()

Passing name strings as arguments

In [7]:
import plotly.express as px
df = px.data.iris()
# Use column names instead. This is the same chart as above.
fig = px.scatter(df, x='sepal_length', y='sepal_width', color='species', size='petal_length')
fig.show()

Using the index of a DataFrame

In addition to columns, it is also possible to pass the index of a DataFrame as argument. In the example below the index is displayed in the hover data.

In [8]:
import plotly.express as px
df = px.data.iris()
fig = px.scatter(df, x=df.sepal_length, y=df.sepal_width, size=df.petal_length,
                 hover_data=[df.index])
fig.show()

Columns not in the data_frame argument

In the addition to columns from the data_frame argument, one may also pass columns from a different DataFrame, as long as all columns have the same length. It is also possible to pass columns without passing the data_frame argument.

However, column names are used only if they correspond to columns in the data_frame argument, in other cases, the name of the keyword argument is used. As explained below, the labels argument can be used to set names.

In [9]:
import plotly.express as px
import pandas as pd
df1 = pd.DataFrame(dict(time=[10, 20, 30], sales=[10, 8, 30]))
df2 = pd.DataFrame(dict(market=[4, 2, 5]))
fig = px.bar(df1, x=df1.time, y=df2.market, color=df1.sales)
fig.show()

Using labels to pass names

The labels argument can be used to override the names used for axis titles, legend entries and hovers.

In [10]:
import plotly.express as px
import pandas as pd

df = px.data.gapminder()
gdp = df['pop'] * df['gdpPercap']
fig = px.bar(df, x='year', y=gdp, color='continent', labels={'y':'gdp'},
             hover_data=['country'],
             title='Evolution of world GDP')
fig.show()

Input Data as array-like columns: NumPy arrays, lists...

px arguments can also be array-like objects such as lists, NumPy arrays, in both long-form or wide-form (for certain functions).

In [11]:
import plotly.express as px

# List arguments
fig = px.line(x=[1, 2, 3, 4], y=[3, 5, 4, 8])
fig.show()
In [12]:
import numpy as np
import plotly.express as px

t = np.linspace(0, 10, 100)
# NumPy arrays arguments
fig = px.scatter(x=t, y=np.sin(t), labels={'x':'t', 'y':'sin(t)'}) # override keyword names with labels
fig.show()

List arguments can also be passed in as a list of lists, which triggers wide-form data processing, with the downside that the resulting traces will need to be manually renamed via fig.data[<n>].name = "name".

In [13]:
import plotly.express as px

# List arguments in wide form
series1 = [3, 5, 4, 8]
series2 = [5, 4, 8, 3]
fig = px.line(x=[1, 2, 3, 4], y=[series1, series2])
fig.show()

Passing dictionaries or array-likes as the data_frame argument

The column-based argument data_frame can also be passed with a dict or array. Using a dictionary can be a convenient way to pass column names used in axis titles, legend entries and hovers without creating a pandas DataFrame.

In [14]:
import plotly.express as px
import numpy as np
N = 10000
np.random.seed(0)
fig = px.density_contour(dict(effect_size=5 + np.random.randn(N),
                              waiting_time=np.random.poisson(size=N)),
                         x="effect_size", y="waiting_time")
fig.show()

Integer column names

When the data_frame argument is a NumPy array, column names are integer corresponding to the columns of the array. In this case, keyword names are used in axis, legend and hovers. This is also the case for a pandas DataFrame with integer column names. Use the labels argument to override these names.

In [15]:
import numpy as np
import plotly.express as px

ar = np.arange(100).reshape((10, 10))
fig = px.scatter(ar, x=2, y=6, size=1, color=5)
fig.show()

Mixing dataframes and other types

It is possible to mix DataFrame columns, NumPy arrays and lists as arguments. Remember that the only column names to be used correspond to columns in the data_frame argument, use labels to override names displayed in axis titles, legend entries or hovers.

In [16]:
import plotly.express as px
import numpy as np
import pandas as pd

df = px.data.gapminder()
gdp = np.log(df['pop'] * df['gdpPercap'])  # NumPy array
fig = px.bar(df, x='year', y=gdp, color='continent', labels={'y':'log gdp'},
             hover_data=['country'],
             title='Evolution of world GDP')
fig.show()

What About Dash?

Dash is an open-source framework for building analytical applications, with no Javascript required, and it is tightly integrated with the Plotly graphing library.

Learn about how to install Dash at https://dash.plot.ly/installation.

Everywhere in this page that you see fig.show(), you can display the same figure in a Dash application by passing it to the figure argument of the Graph component from the built-in dash_core_components package like this:

import plotly.graph_objects as go # or plotly.express as px
fig = go.Figure() # or any Plotly Express function e.g. px.bar(...)
# fig.add_trace( ... )
# fig.update_layout( ... )

import dash
import dash_core_components as dcc
import dash_html_components as html

app = dash.Dash()
app.layout = html.Div([
    dcc.Graph(figure=fig)
])

app.run_server(debug=True, use_reloader=False)  # Turn off reloader if inside Jupyter