Annotated Heatmap

import pandas as pd
import numpy as np

from plotnine import (
    ggplot,
    aes,
    geom_tile,
    geom_text,
    scale_y_reverse,
    scale_y_discrete,
    scale_fill_brewer,
    scale_color_manual,
    coord_equal,
    theme,
    theme_void,
    element_blank,
    element_rect,
    element_text,
)

Conditinous data recorded at discrete time intervals over many cycles

Read data

flights = pd.read_csv("data/flights.csv")
months = flights["month"].unique()  # Months ordered January, ..., December
flights["month"] = pd.Categorical(flights["month"], categories=months)
flights.head()

	year	month	passengers
0	1949	January	112
1	1949	February	118
2	1949	March	132
3	1949	April	129
4	1949	May	121

# We use 'factor(year)' -- a discrete -- instead of 'year' so that all the years
# are displayed along the x-axis.
# The .95s create spacing between the tiles.

(
    ggplot(flights, aes("factor(year)", "month", fill="passengers"))
    + geom_tile(aes(width=0.95, height=0.95))
    + geom_text(aes(label="passengers"), size=9)
)

That looks like what we want, but it could do with a few tweaks. First the contrast between the tiles and the text is not good for the lower passenger numbers. We use pd.cut to partition the number of passengers into two discrete groups.

flights["p_group"] = pd.cut(
    flights["passengers"], (0, 300, 1000), labels=("low", "high")
)
flights.head()

	year	month	passengers	p_group
0	1949	January	112	low
1	1949	February	118	low
2	1949	March	132	low
3	1949	April	129	low
4	1949	May	121	low

(
    ggplot(flights, aes("factor(year)", "month", fill="passengers"))
    + geom_tile(aes(width=0.95, height=0.95))
    + geom_text(aes(label="passengers", color="p_group"), size=9, show_legend=False)  # modified
    + scale_color_manual(["white", "black"])  # new
)

Last tweaks, put January at the top and remove the axis ticks and plot background.

(
    ggplot(flights, aes("factor(year)", "month", fill="passengers"))
    + geom_tile(aes(width=0.95, height=0.95))
    + geom_text(aes(label="passengers", color="p_group"), size=9, show_legend=False)
    + scale_color_manual(["white", "black"])  # new
    + scale_y_discrete(limits=months[::-1])  # new
    + theme(  # new
        axis_ticks=element_blank(),
        panel_background=element_rect(fill="white"),
    )
)

You can get similar results if you replace

 + geom_tile(aes(width=.95, height=.95))
 + geom_text(aes(label='passengers', color='p_group'), size=9, show_legend=False)

with

+ geom_label(aes(label='passengers', color='p_group'), size=9, show_legend=False)

Credit: This example is a recreation of this seaborn example.